Decimal expansion of rational numbers

Correct answer: B. (2^3\cdot 5)

Explanation: Step 1: (0.0075=\frac{75}{10000}). Step 2: Reducing gives (\frac{3}{400}), and (400=2^4\cdot 5^2). This factorisation is not present in the listed choices, so the options have an error. Step 3: Do not choose an option before writing the final denominator in prime factor form.

Correct answer: B. (400)

Explanation: Step 1: (0.0075=\frac{75}{10000}). Step 2: Reducing by (25) gives (\frac{3}{400}). So the denominator is (400). Step 3: Even with many zeros in a decimal, find the greatest common factor carefully.

Correct answer: B. (\frac{1}{28})

Explanation: Step 1: View the denominator in terms of (2), (5), and other factors. Step 2: (28=2^2\cdot 7), so the power (2) of (2) gives a delay of two places before the recurring part starts. The other options give a delay of (1) or a different case. Step 3: The delay before repetition is linked to the larger power of (2) and (5).

Correct answer: D. (8)

Explanation: Step 1: (625=5^4). Step 2: After cancellation, the denominator becomes (2^8\cdot 5^2). The larger exponent is (8), so the decimal terminates after (8) places. Step 3: The numerator may cancel powers of (5), but a larger power of (2) may still remain.

Correct answer: A. The decimal will terminate

Explanation: Step 1: (10^5=2^5\cdot 5^5). Step 2: Any divisor of it contains only powers of (2) and (5). Therefore (\frac{p}{q}) has a terminating decimal. Step 3: Being a divisor gives at most (5) places, not necessarily exactly (5).

Correct answer: A. Terminating

Explanation: Step 1: (0.\overline{81}=\frac{81}{99}) and (0.\overline{18}=\frac{18}{99}). Step 2: Their sum is (\frac{99}{99}=1), which is terminating. Step 3: The sum of two recurring decimals can be terminating.

Correct answer: C. (625)

Explanation: Step 1: For exactly (4) decimal places, the larger power of (2) or (5) in the reduced denominator must be (4). Step 2: (625=5^4), so it gives exactly (4) places. (80=2^4\cdot 5) also gives (4) places, so the choices would need checking if only one answer is expected. Step 3: Factorise all options in such questions.

Correct answer: D. (125)

Explanation: Step 1: For exactly (4) places, the larger exponent must be (4). Step 2: (16=2^4), (625=5^4), and (80=2^4\cdot 5) give exactly (4) places. (125=5^3) gives only (3) places. Step 3: For exact places, the larger exponent must match the required number.

Correct answer: A. (15)

Explanation: Step 1: Let (x=2.4666\ldots). Step 2: (10x=24.666\ldots) and (100x=246.666\ldots), so (90x=222) and (x=\frac{222}{90}=\frac{37}{15}). Step 3: Align the recurring parts before subtracting.

Correct answer: B. Non-terminating recurring

Explanation: Step 1: (98=2\cdot 7^2). Step 2: After cancellation, the denominator becomes (5\cdot 7). Since (7) remains, the decimal is non-terminating recurring. Step 3: Check whether the whole power cancels or only part of it cancels.

Correct answer: B. (\frac{1}{1250})

Explanation: Step 1: (0.0008=\frac{8}{10000}). Step 2: Dividing by (8) gives (\frac{1}{1250}). Step 3: First form the denominator as a power of (10), then reduce.

Correct answer: C. (\frac{1}{72})

Explanation: Step 1: The larger power of (2) or (5) in the denominator tells the delay before the recurring part starts. Step 2: (72=2^3\cdot 3^2), so it has a delay of (3) places. The others have larger exponent (1) or (2). Step 3: Understand the initial non-repeating part in non-terminating recurring decimals.

Correct answer: A. Only (2) and (5) can occur

Explanation: Step 1: For a terminating decimal, the reduced denominator (q) can contain only (2) and (5). Step 2: In (q^2), the powers of the same primes increase, but no new prime factor appears. Step 3: Powers may change, but the prime types do not.

Correct answer: B. (0.25)

Explanation: Step 1: When (9)'s continue forever at the end, the number may equal the next terminating decimal. Step 2: (0.24999\ldots=0.25). Step 3: Convert infinite repeating (9)'s into the simpler terminating form.

Correct answer: D. (2^4\cdot 5\cdot 23)

Explanation: Step 1: For a non-terminating recurring decimal, the reduced denominator must have a prime factor other than (2) and (5). Step 2: (2^4\cdot 5\cdot 23) contains (23). Hence it gives a non-terminating recurring decimal. Step 3: Even one extra prime factor prevents termination.

Correct answer: C. (6)

Explanation: Step 1: The numerator (3^2\cdot 5) cancels from the denominator. Step 2: The reduced denominator is (2^6\cdot 5^3). The larger exponent is (6), so the decimal terminates after (6) places. Step 3: Look for the larger exponent only after cancellation.

Correct answer: A. Rational number

Explanation: Step 1: The block (357) repeats in a fixed way. Step 2: A fixed recurring decimal can always be written as a rational number. Step 3: Identify rationality when a repeating block is fixed.

Correct answer: A. (q=2^4\cdot 5^3)

Explanation: Step 1: A decimal terminates when the reduced denominator contains only (2) and (5). Step 2: (q=2^4\cdot 5^3) satisfies this condition. The other options contain (3), (7), or (11). Step 3: Check the prime factors of the denominator carefully.

Correct answer: A. (2^3\cdot 5^2)

Explanation: Step 1: (27=3^3). Step 2: The full factor (3^3) cancels from the denominator, leaving (2^3\cdot 5^2). Step 3: Decide the decimal type from the denominator left after cancellation.

Correct answer: D. (2200)

Explanation: Step 1: (0.00\overline{45}=0.00454545\ldots). Step 2: It equals (\frac{45}{9900}=\frac{1}{220}). So the denominator is (220). Step 3: Choose the denominator only after reducing.

Correct answer: A. (220)

Explanation: Step 1: (0.00\overline{45}) has two non-repeating zeros and two repeating digits. Step 2: Its fraction form is (\frac{45}{9900}), which reduces to (\frac{1}{220}). Step 3: The first denominator formed from a recurring decimal may not be the final denominator.

Correct answer: B. Non-terminating recurring

Explanation: Step 1: (\frac{18}{999}=\frac{2}{111}). Step 2: (111=3\cdot 37), which has factors other than (2) and (5). Therefore the decimal is non-terminating recurring. Step 3: Fractions from recurring decimals often have denominators made from (9)'s.

Correct answer: D. (50)

Explanation: Step 1: For exactly (2) places, the larger exponent must be (2). Step 2: (4=2^2), (20=2^2\cdot 5), and (25=5^2) give exactly (2) places. (50=2\cdot 5^2) also gives exactly (2) places, so none of the listed choices is impossible. Step 3: If all options seem possible, check the question or options for an error.

Correct answer: C. (5)

Explanation: Step 1: (45=3^2\cdot 5). Step 2: After cancellation, the denominator becomes (2^5\cdot 5^3). The larger exponent is (5), so the decimal terminates after (5) places. Step 3: Always reduce the fraction before counting decimal places.

Correct answer: A. (36)

Explanation: Step 1: Let (x=0.027777\ldots). Step 2: (100x=2.7777\ldots) and (1000x=27.7777\ldots), so (900x=25) and (x=\frac{25}{900}=\frac{1}{36}). Step 3: For a mixed recurring decimal, separate the non-repeating and repeating parts before multiplying.