What number should replace the question mark in the series given below? 55, 47, 74, 10, 135, -81, 262, ?

A774

B-250 ✓ Correct

C343

D-343

Correct answer: (B) -250

Explanation

The next number is -250.

Add and subtract successive cubes with alternating signs.

-2^3, +3^3, -4^3, +5^3, -6^3, +7^3, then -8^3.

55 - 8 = 47, 47 + 27 = 74, 74 - 64 = 10, 10 + 125 = 135.

135 - 216 = -81, -81 + 343 = 262, 262 - 512 = -250.

Method: alternating cubes 2^3 to 8^3.

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