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What is 3/4 + 5/6?
Correct answer: C. 1 7/12
Use the least common denominator, 12: 3/4 = 9/12 and 5/6 = 10/12. Then 9/12 + 10/12 = 19/12 = 1 7/12. Adding numerators and denominators directly (8/10) is a common mistake.
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Basic Operations and Number Sequence MCQs
Civil Service Exam numerical ability reviewer: fractions, decimals, percentages, order of operations, LCM and GCF, powers and roots, and number sequences, all solved without a calculator.
20 MCQsUpdated 3 November 2026
Numerical Ability is tested in both levels of the Civil Service Exam, and its official scope covers basic operations, number sequence and word problems. This set practises the first two: fractions, decimals and percentages, the order of operations, LCM and GCF, powers and square roots, and number sequences built on differences, ratios and other patterns.
Calculators are not allowed in the exam, so work each item by hand and use the shortcuts in the explanations, such as finding 15% as 10% plus 5%. Every answer here was calculated and checked by script.
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What is 2 1/2 × 1 3/5?
Correct answer: A. 4
Change to improper fractions: 2 1/2 = 5/2 and 1 3/5 = 8/5. Then 5/2 × 8/5 = 40/10 = 4. Multiplying the whole numbers and fractions separately gives a wrong answer.
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What is 7.25 − 3.875?
Correct answer: D. 3.375
Line up the decimal points and add a zero: 7.250 − 3.875 = 3.375. Check by adding back: 3.875 + 3.375 = 7.25. Lining up the decimal points is the step most often skipped under time pressure.
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What is 0.6 × 0.15?
Correct answer: B. 0.09
Multiply as whole numbers, 6 × 15 = 90, then count the decimal places: one in 0.6 and two in 0.15 make three, so the answer is 0.090 = 0.09.
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What is 15% of 840?
Correct answer: A. 126
15% of 840 = 0.15 × 840 = 126. A quick way without a calculator: 10% is 84 and 5% is 42, so 15% is 84 + 42 = 126. Splitting a percentage into easy parts like this is useful because calculators are not allowed.
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48 is what percent of 160?
Correct answer: B. 30%
Percent = part ÷ whole × 100 = 48 ÷ 160 × 100 = 30%. Check: 30% of 160 = 48. A shortcut: 48/160 simplifies to 3/10 by dividing both numbers by 16, and 3/10 is 30%.
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Simplify: 12 + 18 ÷ 3 × 2 − 4
Correct answer: D. 20
Do division and multiplication first, from left to right: 18 ÷ 3 = 6, then 6 × 2 = 12. Then add and subtract from left to right: 12 + 12 − 4 = 20.
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What is (−8) × (−3) − (−5)?
Correct answer: A. 29
A negative times a negative is positive: (−8) × (−3) = 24. Subtracting a negative is the same as adding: 24 − (−5) = 24 + 5 = 29.
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What is 2/3 of 3/4 of 480?
Correct answer: B. 240
"Of" means multiply: 3/4 × 480 = 360, then 2/3 × 360 = 240. Or multiply the fractions first: 2/3 × 3/4 = 1/2, and half of 480 is 240.
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Which of the following is the largest?
Correct answer: B. 5/8
Convert all to decimals: 0.6, 5/8 = 0.625, 3/5 = 0.6 and 0.58. The largest is 0.625, which is 5/8. Note that 0.6 and 3/5 are equal.
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What is the least common multiple (LCM) of 12, 18 and 24?
Correct answer: C. 72
Prime factors: 12 = 2² × 3, 18 = 2 × 3², 24 = 2³ × 3. Take the highest power of each prime: 2³ × 3² = 72. Check: 72 is divisible by 12, 18 and 24.
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What is the greatest common factor (GCF) of 84 and 126?
Correct answer: D. 42
84 = 2² × 3 × 7 and 126 = 2 × 3² × 7. The common factors with the lowest powers are 2 × 3 × 7 = 42. Check: 84 ÷ 42 = 2 and 126 ÷ 42 = 3.
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What is 3⁴ − 4³?
Correct answer: D. 17
3⁴ = 3 × 3 × 3 × 3 = 81 and 4³ = 4 × 4 × 4 = 64. So 81 − 64 = 17. Be careful not to mix up the base and the exponent: 3⁴ means 3 multiplied by itself four times, not 3 × 4.
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What is √144 + √81?
Correct answer: A. 21
√144 = 12 and √81 = 9, so the sum is 21. Note that √144 + √81 is not √225 (= 15): square roots cannot be added by adding the numbers under the root sign.
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What number comes next: 5, 11, 23, 47, ___?
Correct answer: D. 95
Each term is double the previous term plus 1: 5 × 2 + 1 = 11, 11 × 2 + 1 = 23, 23 × 2 + 1 = 47, so 47 × 2 + 1 = 95. When the terms roughly double each time, test a rule of the form "× 2 plus or minus a small number".
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What number comes next: 81, 27, 9, 3, ___?
Correct answer: B. 1
Each term is the previous term divided by 3: 81 ÷ 3 = 27, 27 ÷ 3 = 9, 9 ÷ 3 = 3, so 3 ÷ 3 = 1. This is a geometric sequence with ratio 1/3.
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What number comes next: 1, 4, 9, 16, 25, ___?
Correct answer: C. 36
These are the perfect squares 1², 2², 3², 4², 5², so the next is 6² = 36. The differences 3, 5, 7, 9 (odd numbers) give the same result: 25 + 11 = 36.
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What number comes next: 3, 4, 7, 11, 18, ___?
Correct answer: A. 29
From the third term on, each term is the sum of the two before it: 3 + 4 = 7, 4 + 7 = 11, 7 + 11 = 18, so 11 + 18 = 29. This is the same rule as the Fibonacci sequence, but with different starting numbers.
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What number comes next: 100, 96, 88, 76, 60, ___?
Correct answer: B. 40
The differences are 4, 8, 12 and 16, increasing by 4 each time, so the next difference is 20: 60 − 20 = 40. Writing the differences under the series is the quickest first step in any sequence item.
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What number comes next: 2, 3, 5, 7, 11, 13, ___?
Correct answer: A. 17
These are the prime numbers in order, numbers with exactly two factors. After 13, the next prime is 17, since 14 = 2 × 7, 15 = 3 × 5 and 16 = 2⁴ are not prime.
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