Population Growth

Correct answer: B. Final population is 125 percent of initial population

A 25 percent increase means the increase is one-quarter of the initial population. Consequently, the final population equals the initial population plus 25 percent of it, or 125 percent of the initial population. Thus choice B is definitely correct.

The statement does not tell us that growth was exactly 2.5 percent in every year. Annual rates may vary and still produce a total ten-year increase of 25 percent. It also does not reveal the birth rate or prove that migration was zero, because total population change can result from births, deaths, immigration, and emigration together. Only the relationship between the initial and final population is certain: final population = 1.25 times initial population.

Correct answer: B. A lower rate on a large population base can still add many people

A growth rate is a percentage applied to the population base, while absolute growth is the actual number of people added. These two measures can move differently. When the starting population is very large, even a smaller percentage can represent a large number of people. Thus, a falling rate does not automatically mean that the annual numerical increase becomes small immediately.

For example, 1.5 percent of a very large population may still be millions of people. Therefore, option B is correct: a lower rate on a large population base can continue to add many people. The question does not imply that birth rates rose, deaths stopped, or land area expanded. Those factors are either unsupported or unrelated to the mathematical reason for a large absolute increase.

Correct answer: B. Young people entering reproductive ages can keep total births high

Fertility rate describes the average number of children born per woman, while total births also depend on how many women are in reproductive ages. A country may therefore experience falling fertility but still have many births if a very large young population is entering or already in those ages. This is called population momentum: the age structure can keep growth continuing for some time.

Thus option B is correct. A lower fertility rate does not immediately reduce the total number of births when the number of potential parents is unusually large. The other choices are unsupported: death rates will not necessarily be zero, migration is not automatically positive, and land area does not expand because of population structure. The key is the large cohort of young people.

Correct answer: C. +2 per thousand

Natural change is found by subtracting the death rate from the birth rate. Here it is \(16-21=-5\) per thousand, so deaths exceed births by 5 per thousand. Net migration is positive at +7 per thousand, meaning arrivals exceed departures by 7 per thousand. Total growth combines natural change and net migration: \(-5+7=+2\) per thousand.

Therefore, option C is correct. The positive migration balance more than offsets the natural decrease, so the country's total population still grows by 2 persons per thousand population during the stated period. Option B represents only natural change, while option D represents only migration and leaves out the birth–death balance. All rates use the same per-thousand unit.

Correct answer: B. -6 per thousand

Total population growth rate is the sum of natural increase and net migration rate. Rearranging the relationship gives net migration rate = total growth rate − natural increase rate. The values are +3 per thousand for total growth and +9 per thousand for natural increase.

Therefore, net migration rate = \(3 - 9 = -6\) per thousand, so option B is correct. The negative sign is important: it means the country loses more people through outward migration than it gains through inward migration. Natural increase is still positive, but the larger negative migration balance reduces total growth from +9 to +3 per thousand.

Correct answer: A. Natural increase will remain positive

Natural population change is determined by the difference between births and deaths, not by whether both rates are rising or falling. If the birth rate remains higher than the death rate, more people are born than die. Natural increase therefore remains positive, although the amount of increase may become smaller if the gap narrows.

Option A is correct. A decline in both rates does not automatically produce a negative change. Migration could alter the total population, but it is not needed to determine the direction of natural change asked here. Option B reverses the meaning of the rate difference, option C assumes stabilization without evidence, and option D confuses natural change with total change including migration.

Correct answer: A. From 20 to 14 per thousand

Natural increase rate is calculated by subtracting the death rate from the birth rate. Initially, it is \(30-10=20\) per thousand. After the changes, it is \(22-8=14\) per thousand. Therefore the natural increase rate falls from 20 to 14 per thousand, making option A correct.

Although both birth and death rates decrease, they do not decrease by the same amount: births fall by 8 per thousand, while deaths fall by only 2 per thousand. The difference between births and deaths consequently becomes smaller by 6 per thousand. The answer is not based on adding the rates; natural increase always uses birth rate minus death rate. Migration is not involved in this calculation.

Correct answer: B. Youth out-migration can reduce future births and growth potential

Population momentum is the tendency for population to keep growing because a large number of young people are reaching reproductive ages. However, this potential depends on those young adults remaining in the country and forming families there. If many of them migrate out, the number of future parents within the country can fall, reducing future births and weakening the expected momentum.

Therefore, option B is correct. The word “can” is important because the exact effect depends on the number and characteristics of migrants, as well as fertility and migration patterns. Population momentum is not necessarily strengthened merely because the country has many young people. Option C is incorrect because concentrated youth out-migration can have a real demographic effect; the other options are unrelated or absolute claims.

Correct answer: A. When the magnitudes of the two are equal

Total population change is the sum of natural increase and net migration. Natural increase equals births minus deaths. If natural increase is negative, the population is losing people naturally. Positive net migration can offset that loss, but for the total population to remain unchanged, the gain from migration must exactly equal the natural decrease.

For example, if natural change is \(-5,000\) and net migration is \(+5,000\), the total change is \(-5,000+5,000=0\). Therefore, option A is correct: the magnitudes must be equal and the signs opposite. If migration were smaller, population would fall; if it were larger, population would rise. Births being zero alone does not establish stability.

Correct answer: C. 240000

A natural increase rate of 12 per thousand means that 12 people are added naturally for every 1,000 people in one year. The population is 20 million, or 20,000,000. Therefore the natural increase is \(20{,}000{,}000\times\frac{12}{1000}=240{,}000\) people. Since migration is zero, this is also the total population increase for the year. Option C is correct.

The rate must be converted from per thousand into a fraction before multiplying. Dividing by 1,000 gives 0.012, or 1.2%; multiplying that by 20 million gives 240,000. The answer is not 12,000 because the base is much larger than one million, and it is not 1,200,000 because that would use a much higher rate. The result is approximate because the rate is stated as an annual demographic rate.

Correct answer: C. Decrease of 120000

A natural increase rate of -3 per thousand means that natural change is a loss of 3 people for every 1000 people. The negative sign is important: it indicates that deaths exceed births, excluding migration. To find the number, multiply the population by \(-3\div1000\).

For 40 million people, the change is \(40000000\times(-3\div1000)=-120000\). Thus, the population experiences an approximate natural decrease of 120000 people in one year. Option C is correct. The result is not a total population change because migration has not been included.

Correct answer: C. +0.6 percent

Total population growth is the sum of natural growth and net migration. Natural growth is already −1%, meaning births and deaths together cause a one-percent decline. Net migration is +1.6%, meaning immigration exceeds emigration by 1.6% of the population.

Add the rates with their signs: −1% + 1.6% = +0.6%. Thus migration more than compensates for the natural decline, and the total population grows by 0.6%. Therefore option C is correct. The negative sign must remain attached to natural growth, but the larger positive migration rate makes the final result positive.

Correct answer: A. Large cohorts born earlier are still passing through school ages

Population structure changes gradually because people born in earlier years continue to move through the age groups. A fall in fertility affects the number of young children first, but it does not immediately remove a large group that was already born. If that earlier group is large, many of its members may remain in school ages for several years.

Therefore, option A is correct: large cohorts born earlier are still passing through school ages. This is called a time-lag effect in age structure. School systems may continue to face high demand even after fertility declines. The other choices are not valid explanations: schools do not necessarily raise birth rates, death rates are not zero, and migration does not always increase the number of children.

Correct answer: B. Demand for elderly care and pensions may increase

A shrinking child population and a growing elderly population indicate demographic ageing. Over time, this pattern can reduce the number of people needing primary schools while increasing the number needing health services, assisted living, long-term care, and pension support. The working-age population may also face greater responsibility for supporting older people. Therefore, option B identifies the most likely long-term challenge.

The word “may” is important because the exact effects depend on migration, policy, health, retirement age, and employment patterns. Greater school pressure is not necessary when the number of children is falling. Birth rates do not automatically rise, and the working-age group will not always grow. The clearest direct implication is increased demand for elderly care and pensions.

Correct answer: B. When the growth rate changes rapidly over time

The Rule of 70 works best when the annual growth rate remains approximately constant. It treats the stated rate as if it continues throughout the whole period. If the rate changes substantially, the population will not follow the simple path assumed by the rule, so the estimated doubling time may differ from the actual time.

A rate of 1 percent gives an approximate doubling time of \(70\div1=70\) years. However, if fertility, mortality, or migration causes the rate to change rapidly, that estimate becomes less reliable. A large population alone does not invalidate the rule, and both births and deaths occur in any normal population. Therefore option B is correct.

Correct answer: B. 16.64 percent

When the same annual growth rate applies repeatedly, the second year acts on the population already increased during the first year. This is compound growth, not simple addition. Therefore, the second 8 percent is calculated on 108 percent of the original population.

Starting with population P, after two years it becomes \(P\times1.08\times1.08=P\times1.1664\). The final population is 116.64 percent of the original, so the total increase is 16.64 percent. Hence option B is correct. Adding 8 percent and 8 percent gives 16 percent only as a rough simple-growth estimate and misses the second-year increase on the first year’s gain.

Correct answer: A. The second 10 percent decline applies to a smaller population base

A repeated percentage change is applied to the amount remaining after the previous change, not to the original amount each time. This is why equal annual percentage decreases cannot simply be added. The second decrease has a smaller base than the first one.

For example, start with 100. A 10 percent decrease leaves 90. Ten percent of 90 is 9, so the second year leaves 81. The total fall is 19 from the original 100, or 19 percent, not 20 percent. Therefore, option A is correct. The process can also be written as \(100 \times 0.9 \times 0.9=81\).

Correct answer: A. When most migrants are young working-age adults

Population ageing is measured partly by the share of older people in the total population. If most incoming migrants are young working-age adults, they increase the size of the working-age group. This can reduce the percentage share of elderly people for a while, even if the absolute number of elderly residents does not fall. Young migrants may also have children, affecting the age structure further.

Option A is correct. The question asks when net in-migration can temporarily slow ageing, and the age of migrants is decisive. If migrants are elderly, they may increase rather than reduce the older share. No migration creates no such effect, while migrants who immediately leave do not add lasting population. The word “temporarily” matters because migrants themselves will age over time.

Correct answer: A. Large numbers of working-age people are emigrating

Natural increase concerns births and deaths in the whole population, whereas the working-age group is only one part of the age structure. A country may have more births than deaths and therefore positive natural increase, yet lose many adults through emigration. If those departures are concentrated among working-age people, that group can shrink even while the total population grows.

Births initially add children, not working-age adults, so they do not immediately replace emigrating workers. The result may be a smaller labour force, a lower working-age share, or both. Therefore option A is possible and correct. The other choices are either biologically incorrect or deny the fact that migration and age-selective movement can change the composition of a population.

Correct answer: A. More surviving children can increase future population size

A large child population creates a strong age-structure effect. When child mortality falls, more children who have already been born survive into later childhood, adolescence, and adulthood. This increases the number of people who can form families and join the working-age population in the future. The effect is especially important when fertility does not decline equally quickly.

Thus option A is correct: more surviving children can increase future population size. Population will not necessarily decline immediately, and a lower child mortality rate does not make the birth rate zero. Age structure remains highly relevant because the large young group can produce population momentum even when fertility later falls.

Correct answer: A. Growth likely came more from other age groups or migration

The total population and the age composition do not have to change at the same rate. In this case, total population rises by 20 percent, but the number of children rises by only 5 percent. This means the larger increase must mainly be found among adults, older people, or migrants who are not children. The data do not identify one exact cause, but they support a cautious comparison of age groups.

Therefore, option A is the most appropriate conclusion. A higher total population does not prove that the birth rate doubled, because births are only one influence and the time period and age definitions matter. The number of children did not decline; it increased by 5 percent. Nor is the total figure necessarily wrong. The conclusion should remain probabilistic rather than absolute.

Correct answer: A. Arrivals and departures may be equal

Gross migration describes the total movement into and out of a region. Net migration is the difference between in-migration and out-migration. Therefore, a region can have very high movement while its net migration is zero if the two flows are equal.

For example, if 100,000 people arrive and 100,000 leave, gross migration is very high, but net migration is \(100000-100000=0\). The region has experienced substantial movement, yet the flows have not changed its population overall. Thus arrivals and departures may be equal, making option A correct. Zero net migration does not mean that nobody moved.

Correct answer: C. 900000

A percentage growth rate is applied to the starting population. For a simple one-year increase, multiply the population by the rate written as a decimal. Since 0.75 percent means 0.75 divided by 100, its decimal form is 0.0075. The result is an approximate increase because the question asks for a simple one-year calculation rather than compounding.

The population is 120 million, or 120,000,000. The increase is \(120000000\times0.0075=900000\) people. Thus approximately 900,000 people are added in one year, so option C is correct. The answer is not 9,000 because the rate is applied to 120 million, and not 12 million because 0.75 percent is less than one percent.

Correct answer: A. The age structure may become younger

Net migration records only the numerical difference between people entering and leaving. It does not show whether the two flows have the same age composition. If the number of young in-migrants equals the number of older out-migrants, net migration is zero, but the population receives younger members and loses older members. The age distribution can therefore change even when the total population effect of migration is zero.

Option A is correct because the replacement of older residents by younger adults can make the city’s age structure younger. This does not mean the total population doubles, that natural increase becomes zero, or that no structural effect occurs. Age-selective migration can also affect future births, labour supply, and dependency patterns, although those further effects are not required to answer the question.

Correct answer: A. Population ageing with continuing slower growth

A falling birth rate generally reduces the share of children entering the population and can gradually raise the average age. However, total population does not necessarily stop growing immediately. A large young population from earlier periods can continue entering childbearing ages, producing demographic momentum. Lower mortality or positive migration may also support continued growth.

The combined pattern is therefore population ageing with continuing slower growth, so option A is correct. It is not high fertility and rejuvenation because births are declining. It is not complete stability because total population is still increasing. The statement does not require rapid natural increase; it describes ageing together with a continuing but slower rise.