Population Density

Correct answer: B. 600 square kilometres

Explanation: Answer: B, 600 square kilometres. Begin with density = population ÷ area. To find area, rearrange the formula: area = population ÷ density. Substitution gives 90,000 ÷ 150 = 600 square kilometres. The units also support the answer: people divided by people per square kilometre leaves square kilometres. A, 450, would imply a density of 200 persons per square kilometre, not 150. C would give a lower density of 120, and D would give 100. Thus these values do not satisfy the stated relationship. A useful check is to multiply the proposed area by 150; only 600 × 150 returns 90,000. Remember the formula triangle: population is density times area, so area is population divided by density.

Correct answer: B. The city

Explanation: Answer: B, the city. Population density is the number of people per square kilometre. Both figures use the same unit, so they can be compared directly: 500 is greater than 100. This means the city has a greater average concentration of people in each square kilometre. A is wrong because the village has the smaller numerical density. C is wrong because 500 and 100 are not equal. D is wrong because comparison is possible when the units are the same; different units would need conversion, but no conversion is needed here. This conclusion does not mean the city must have a larger total population, because total population also depends on area. It only means that people are more concentrated per unit area. Memory cue: compare density numbers only after checking that their units match.

Correct answer: B. It will increase

Explanation: When the area stays fixed, density depends directly on the population. More people distributed over the same amount of land produce a higher average density. The question asks only for the direction of change, not for a numerical value, because the area has not been supplied. Therefore we compare the old and new populations rather than trying to calculate an exact density.

The population rises from 100000 to 120000, an increase of 20000 people. Since the denominator, or area, is unchanged, the quotient population divided by area must increase. Hence option B is correct. Density cannot decrease, remain the same, or become zero when the number of people increases and the area remains positive. The exact new value would require the common area.

Correct answer: B. Density may decrease

Explanation: Population density is calculated by dividing population by area. If people leave a region and its area does not change, the number in the numerator becomes smaller. As a result, fewer people are distributed over the same amount of land, so the density generally decreases. The exact size of the decrease depends on how many people leave.

Thus, out-migration can reduce density, making option B correct. The word “may” is important because the question does not give the number of migrants, and other population changes could occur at the same time. Density cannot be said to remain unchanged, double, or follow any fixed amount. In-migration would have the opposite effect if more people entered the region.

Correct answer: A. It can increase

Explanation: Population density depends on the number of people and the area they occupy. When many people move into a city for jobs, the city’s population increases. If the administrative area remains unchanged, the same land must accommodate more residents, so the average number of people per square kilometre rises. This is an example of how migration can change population distribution even without any change in the physical size of the city.

Option A is correct because employment-related inward migration can increase density. The increase is not guaranteed if people leave at the same time, if the boundary expands, or if the incoming population is counted outside the city; therefore “can increase” is the careful wording. Density cannot automatically fall to zero, always remain unchanged, or cause the area to double. Options B, C, and D make absolute or physically incorrect claims.

Correct answer: A. Unit of measurement

Explanation: A density value is meaningful only when the quantities being compared use compatible units. Population density may be expressed as persons per square kilometre, persons per square mile, or another area unit. A value stated per square kilometre cannot be compared directly with one stated per square mile because the size of the land unit differs. The values must first be converted to the same area basis, while the population count should also refer to comparable time and boundaries.

Option A is therefore correct. Language, the country’s name, and the size of its capital do not determine whether two density measurements can be mathematically compared. For instance, two regions may have identical populations but different densities because their areas differ. If one figure is per square mile and another per square kilometre, direct ranking may be misleading. Converting both to a common unit makes the comparison valid and prevents an apparent difference caused only by measurement convention.

Correct answer: B. 200 persons per square kilometre

Explanation: Arithmetic population density is calculated by dividing population by land area. This measure gives the average number of people living in one square kilometre, so the answer must have the unit persons per square kilometre. The number used as area is a divisor, not the density itself.

The calculation is \(200000\div1000=200\) persons per square kilometre. Hence option B is correct. Choosing 1000 would confuse the given area with the calculated density, while 100 and 500 do not match the quotient. The result means that each square kilometre contains 200 people on average, not that every part has exactly that number.

Correct answer: C. 500 persons per square kilometre

Explanation: Answer: C, 500 persons per square kilometre. Apply the formula density = population ÷ area. Therefore, density = 35,000 ÷ 70. Cancel one zero from both numbers to get 3,500 ÷ 7, which equals 500. The unit is persons per square kilometre because people are divided by square kilometres. A, 350, results from an arithmetic error and is too low. B, 400, does not equal the quotient. D, 700, may arise from reversing or mishandling the numbers, but it is not the correct division. Always identify the numerator and denominator before calculating: population goes on top and area goes below. A quick check is 500 × 70 = 35,000, confirming the result.

Correct answer: B. Region with 250

Explanation: Density is a measure of how many people occupy a unit of area. When two density figures are expressed in the same unit, they can be compared directly by their numerical values. A larger number means more people, on average, are present in each square kilometre. No extra information about total population or total area is needed for this comparison.

Here, 250 persons per square kilometre is greater than 200 persons per square kilometre. Therefore, the region with 250 has the higher density, so option B is correct. Option A reverses the comparison, while option C is incorrect because the values are not equal. Option D is also wrong: comparison is possible precisely because both values have the same unit.

Correct answer: B. 500 square kilometres

Explanation: The relationship between population, density, and area is \(D=\frac{P}{A}\). To find area, rearrange it as \(A=\frac{P}{D}\). Using the given figures, \(A=\frac{60000}{120}=500\) square kilometres. The units also confirm the result: people divided by people per square kilometre leaves square kilometres.

Therefore, option B is correct. A quick check is useful: a density of 120 persons per square kilometre across 500 square kilometres gives \(120\times500=60000\) people. Options A, C, and D do not reproduce the stated total population at the given density, so they cannot be the required area.

Correct answer: A. Zero

Explanation: Population density tells us how many people live in one unit of area. It is calculated by dividing total population by total area. If a region has no residents, its population is zero. Assuming the region has a real, non-zero area, there are zero people in every square kilometre or other unit of area. Therefore, the density is zero, so option A is correct. The area itself does not become the density; area is the denominator used in the calculation.

Using the formula, \(\text{Population density}=\frac{\text{Population}}{\text{Area}}\), we get \(\frac{0}{\text{Area}}=0\). Options B and C incorrectly assign positive values even though nobody lives there. Option D confuses area with density. A zero-area case would make the formula undefined, but an ordinary region has non-zero area. Thus the supplied answer and explanation are correct.

Correct answer: B. No, because area also matters

Explanation: Answer: B, no, because area also matters. Population density is calculated as total population divided by total area. A country can have a very large population but also possess a very large area, causing the average number of people per square kilometre to be moderate or low. Conversely, a smaller total population in a very small area may produce high density. A is wrong because total population alone is not enough. C is wrong because birth rate can affect population growth, but it does not by itself determine present density; area must also be considered. D is wrong because the size of a capital city does not describe the population and area of the whole country. Memory cue: total population tells how many people there are; density tells how closely they are distributed over land.

Correct answer: B. No because population also matters

Explanation: Population density means the number of people living in one unit of area. It is not decided by area alone. A small country may have many people and therefore high density, but it may also have very few people and therefore low density. Climate, coast, resources, and development can influence settlement, but none of them gives an automatic answer.

The relevant relationship is density = population ÷ area. Thus, both population and area must be considered together. A small denominator usually raises density only when the numerator, or population, is sufficiently large. Therefore option B is correct. Options A, C, and D are too absolute because they ignore population and claim that every small country must be densely populated.

Correct answer: C. 200 persons per square kilometre

Explanation: Answer: C, 200 persons per square kilometre. Use density = population ÷ area. The calculation is 500,000 ÷ 2,500 = 200. A convenient simplification is to cancel two zeros, giving 5,000 ÷ 25 = 200. The answer unit is persons per square kilometre because the population is divided by an area measured in square kilometres. A, 100, would give only 250,000 people when multiplied by the stated area. B gives 375,000, and D gives 625,000, so neither matches the given population. A useful verification is 200 × 2,500 = 500,000. Be careful not to divide area by population or to treat 2,500 as the density; the formula always places population in the numerator.

Correct answer: C. 60000 people

Explanation: Population density tells us how many people live in one square kilometre. To find the total population, multiply the density by the total area. The units also confirm the method: people per square kilometre multiplied by square kilometres leaves people. Therefore, this is a direct multiplication problem rather than an addition or division problem.

Use \(75\times800\). Multiplying 75 by 8 gives 600, and attaching the two zeros from 800 gives 60,000. Thus the population is 60,000 people, so option C is correct. Option A is too small, option B results from an incorrect multiplication, and option D may arise from confusing the density value with the final population.

Correct answer: C. 90000 people

Explanation: Population density tells us how many people live in one square kilometre. When density and total area are known, total population is found by multiplying them. This works because every square kilometre contains about 180 people, and there are 500 such square kilometres.

Using the formula \(P=D\times A\), we get \(P=180\times500=90,000\) people. Therefore, option C is correct. Options A, B, and D result from using an incorrect multiplication or estimation. The unit also confirms the answer: people per square kilometre multiplied by square kilometres gives people.

Correct answer: A. Because people need not be evenly spread across the region

Explanation: Population density is an average, not a detailed map of where every person lives. It is calculated for the whole region by dividing total population by total area. Within that region, people may be concentrated in towns, valleys, or along transport routes, while other places may have very few residents. The average hides these local differences.

Therefore, it is important to remember that people need not be evenly distributed across the region. Option A is correct. Density does not apply only to cities, and both area and total population are essential to the calculation. The other options incorrectly reject one of these necessary ideas.

Correct answer: B. No because density is an average

Explanation: Average density is a ratio for a whole country: total population divided by total area. An average summarizes a large region and does not require every part of that region to have the same number of people. Some square kilometres may contain cities, with many residents, while others may be forests, deserts, mountains, farms, or water, with few or no residents.

Thus an average of 100 means the country as a whole has 100 persons per square kilometre when its total population is compared with its total area. It does not mean that every individual square kilometre contains exactly 100 people. Therefore option B is correct. Option A wrongly treats an average as an identical local value, and options C and D incorrectly limit the statement to only one type of settlement.

Correct answer: C. 400 persons per square kilometre

Explanation: Population density tells us how many people live in one unit of area. It is found by dividing the total population by the total area. The answer must therefore be expressed as persons per square kilometre. This measure allows populations in regions of different sizes to be compared fairly.

Here, population is 50,000 and area is 125 square kilometres. Thus, density is \(50000\div125=400\) persons per square kilometre. A quick check gives \(125\times400=50000\), confirming the calculation. Therefore, option C is correct. The other values result from using an incorrect divisor or arithmetic.

Correct answer: C. 400 persons per square kilometre

Explanation: Population density tells us how many people live in one unit of area. It is found by dividing the total population by the total area. The unit here is persons per square kilometre, because the population is given in people and the area in square kilometres.

Use the formula \(\text{Density}=\frac{\text{Population}}{\text{Area}}\). Thus, \(\frac{64000}{160}=400\) persons per square kilometre. The division can also be simplified as \(6400\div16=400\). Therefore, option C is correct. Options A, B, and D result from incorrect division or from using the figures without applying the density formula.

Correct answer: C. 80000 people

Explanation: Answer: C, 80,000 people. Population density tells us how many people live in one square kilometre. To find the total population, multiply density by area: Population = Density × Area = 320 persons per square kilometre × 250 square kilometres. The square-kilometre units cancel, leaving persons. Thus, 320 × 250 = 80,000 people. A is incorrect because 320 × 250 is not 60,000. B is also too low and does not result from the multiplication. C is correct because it gives the exact product. D is too high. Memory cue: density multiplied by area gives population; population divided by area gives density.

Correct answer: B. It decreases

Explanation: Population density is the number of people divided by the area they occupy. If the area stays fixed and the number of people increases, the same land must be shared by more people. Therefore, the average land available per person becomes smaller. This describes an average relationship; it does not mean that every individual owns a specific equal piece of land.

Mathematically, land per person is \(Area \div Population\), which is the inverse of density. A higher density therefore means less area per person. Hence option B, “It decreases,” is correct. It cannot be said to increase or become infinite, and it does not always remain unchanged because the population-to-area ratio has changed.

Correct answer: A. Total population and total area

Explanation: Two basic measurements are enough to calculate the average population density of a region: its total population and its total area. The formula is \(Population\ Density=\frac{Total\ Population}{Total\ Area}\). If either value is missing, the average cannot be obtained. The area must refer to the same region as the population, and the units must be kept consistent so that the answer has a meaningful unit such as persons per square kilometre.

Option A supplies exactly these two required pieces of information. Birth and death rates help analyse population change, while rainfall and temperature are environmental factors that may influence settlement. Latitude and longitude locate a place but do not tell us how many people live there or how large the region is. Hence A is correct.

Correct answer: C. 300 persons per square kilometre

Explanation: The density formula is total population divided by total area. It is important to use the area as the divisor and to keep the unit persons per square kilometre. The number 900 is the area, not the answer by itself. A useful check is to multiply the proposed density by the area and see whether it gives the stated population.

Using the values, \(270000 \div 900 = 300\). Therefore the density is 300 persons per square kilometre, so option C is correct. The check \(300 \times 900 = 270000\) confirms the result. Choosing 900 confuses the area with density; 200 and 250 would produce only 180000 and 225000 people over 900 square kilometres, respectively.

Correct answer: B. 500 square kilometres

Explanation: Population density tells us how many people live on one square kilometre. The basic relationship is density = population divided by area. Therefore, when population and density are known, area must be found by dividing population by density. This keeps the units meaningful: people divided by people per square kilometre gives square kilometres.

Here, area = \(120000 \div 240 = 500\) square kilometres. Thus option B is correct. Multiplying 120000 by 240 would not answer the question because that operation would increase the number instead of reversing the density formula. A quick check confirms the result: \(500 \times 240 = 120000\) people.