What should come in place of the question mark (?) in the given series? 32,…

2025

What should come in place of the question mark (?) in the given series?

32, 37, 47, 62, 82, ?

  1. A.

    92

  2. B.

    97

  3. C.

    107

  4. D.

    100

Attempted by 3 students.

Show answer & explanation

Correct answer: C

In a number series where the plain, first-order differences between consecutive terms are not constant, check whether those first differences themselves form a simple arithmetic progression — that is, whether the second-order differences (the differences between the differences) are constant. When they are, the series has quadratic growth: the next first difference equals the last first difference plus that constant second-order difference, and the next term equals the last term plus this next first difference.

  1. Compute the first differences of the given series 32, 37, 47, 62, 82: 37-32=5, 47-37=10, 62-47=15, 82-62=20.

  2. Compute the second differences of these values: 10-5=5, 15-10=5, 20-15=5 — a constant value of 5.

  3. Since the second difference is constant at 5, the next first difference continues the same pattern: 20+5=25.

  4. Add this next difference to the last given term: 82+25=107.

  • The pattern gives a closed form t(n) = 32 + 5×(n-1)×n/2 for the nth term. Checking n=5: 32 + 5×4×5/2 = 32+50 = 82, matching the fifth given term.

  • Checking n=6 with the same formula: 32 + 5×5×6/2 = 32+75 = 107, the same value obtained by the difference method.

The value that replaces the question mark is 107.

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