31 is related to 152 by certain logic. Following the same logic, 47 is related to 168. To which of the following is 66 related, following the same logic? (NOTE : Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding /deleting /multiplying etc., to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)

Correct — B. Test the plain difference before anything cleverer.

Rule: second number = first number + 121.

152 − 31 = 121
168 − 47 = 121

So 66 + 121 = 187 → option (b)

Why the others are wrong

• (a)
  180 — 180 is 66 + 114. The gap is fixed at 121 by both worked pairs, and 114 fits neither of them.
• (c)
  185 — 185 is 66 + 119, two short. A constant-difference rule has no room to drift by two.
• (d)
  190 — 190 is 66 + 124. Again the gap must be 121, the same value that carries 31 to 152 and 47 to 168.

A number analogy asks you to find one operation that carries the first number to the second, and then to apply it unchanged.

Work through the candidates in a fixed order: difference first, then ratio, then squares and cubes with an offset. The difference costs one subtraction and settles this question immediately.

The NOTE is part of the question, not decoration. It bars digit-level operations, so 31 may not be treated as a 3 and a 1.

Key facts

• 152 − 31 = 121 and 168 − 47 = 121, so the two samples share one constant gap.
• 66 + 121 = 187.
• The question's NOTE forbids splitting a number into its digits.

Common traps

• Hunting for a multiplication rule before checking the plain difference
• Breaking 66 into 6 and 6, which the NOTE forbids
• Fixing the rule from one sample pair without checking it against the second

No directly related past PYQ was found.