Number Series Questions and Answers

Answer: C

Correct answer: 62

The gaps are not equal: they run 8, 10, 12, 14, each 2 more than the last. The next gap must therefore be 16, and adding it to the final term, 46 plus 16 is 62. As a check, the gap between the answer and 46 is 16, which continues the run of gaps 8, 10, 12, 14 by a further 2. Where all four options are close together, the arithmetic rather than the rule is what is being tested.

Answer: D

Correct answer: 92

The gaps are not equal: they run 4, 10, 16, 22, each 6 more than the last. The next gap must therefore be 28, and adding it to the final term, 64 plus 28 is 92. As a check, the gap between the answer and 64 is 28, which continues the run of gaps 4, 10, 16, 22 by a further 6. Where the options are widely spread, identifying the family is enough to choose between them without exact calculation.

Answer: A

Correct answer: 86

The gaps are not equal: they run 3, 10, 17, 24, each 7 more than the last. The next gap must therefore be 31, and adding it to the final term, 55 plus 31 is 86. As a check, the gap between the answer and 55 is 31, which continues the run of gaps 3, 10, 17, 24 by a further 7. The rule should account for every term shown, not merely the last two.

Answer: B

Correct answer: 80

The gaps are not equal: they run 6, 9, 12, 15, each 3 more than the last. The next gap must therefore be 18, and adding it to the final term, 62 plus 18 is 80. As a check, the gap between the answer and 62 is 18, which continues the run of gaps 6, 9, 12, 15 by a further 3. A series may be read as a formula in the position or as a step from the previous term, and the two views agree.

Answer: C

Correct answer: 63

The gaps are not equal: they run 7, 9, 11, 13, each 2 more than the last. The next gap must therefore be 15, and adding it to the final term, 48 plus 15 is 63. As a check, the gap between the answer and 48 is 15, which continues the run of gaps 7, 9, 11, 13 by a further 2. Checking parity, whether the terms are odd or even, often eliminates options before any arithmetic is done.

Answer: D

Correct answer: 95

The gaps are not equal: they run 2, 9, 16, 23, each 7 more than the last. The next gap must therefore be 30, and adding it to the final term, 65 plus 30 is 95. As a check, the gap between the answer and 65 is 30, which continues the run of gaps 2, 9, 16, 23 by a further 7. The last gap is usually the largest in a growing series, which sets a lower bound on the answer.

Answer: A

Correct answer: 102

The steps run 6, 9, 21, 9, which grow and then fall back, so a single operation cannot account for them. Two operations are applied in turn, and continuing the alternation from 51 gives 102. As a check, the step from 51 to the answer is 51, which breaks the run of preceding gaps exactly as an alternating rule demands. A term that breaks an otherwise clear pattern is usually a signal of an interleaved series rather than an error.

Answer: B

Correct answer: 292

The steps run 9, 5, 51, 5, which grow and then fall back, so a single operation cannot account for them. Two operations are applied in turn, and continuing the alternation from 73 gives 292. As a check, the step from 73 to the answer is 219, which breaks the run of preceding gaps exactly as an alternating rule demands. Multiplicative series reach large numbers within five or six terms, which is why they are shown with fewer terms.

Answer: C

Correct answer: 77

The steps run 7, 3, 17, 3, 37, which grow and then fall back, so a single operation cannot account for them. Two operations are applied in turn, and continuing the alternation from 74 gives 77. As a check, the step from 74 to the answer is 3, which breaks the run of preceding gaps exactly as an alternating rule demands. An additive series can be extended indefinitely, so the number of terms shown carries no information about the rule.

Answer: D

Correct answer: 430

The steps run 8, 6, 64, 6, which grow and then fall back, so a single operation cannot account for them. Two operations are applied in turn, and continuing the alternation from 86 gives 430. As a check, the step from 86 to the answer is 344, which breaks the run of preceding gaps exactly as an alternating rule demands. Where a rule involves subtraction the series will eventually pass zero, which the options sometimes exploit.