The series given below contains a sequence of numbers. Accordingly identify the incorrect combination.25 , 29 , 37 , 53 , 87

Correct — D.
Rule: the gaps double: +4, +8, +16, +32.

25 + 4 = 29 ✓
29 + 8 = 37 ✓
37 + 16 = 53 ✓
53 + 32 = 85, not 87

So 87 is the incorrect term → option (d).

Why the others are wrong

• (a)
  29 — 29 is 25 + 4, the first gap of the doubling run 4, 8, 16, 32. It fits the rule.
• (b)
  37 — 37 is 29 + 8, twice the first gap. It fits, and so does the step after it (37 + 16 = 53).
• (c)
  53 — 53 is 37 + 16, exactly the rule's third gap. The break comes after it: 87 − 53 = 34, where the rule needs 32.

In a wrong-term item, find the rule that most terms obey, then locate the term that breaks it.

Here the gaps 4, 8, 16 each double the last, so the fourth gap should be 32. 53 + 32 = 85, and the series prints 87, two too many.

Key facts

• Gaps here: 4, 8, 16, 32, each double the last.
• A series whose gaps double can also be written × 2 + c, here with c = −21.
• The gap into 53 (16) fits, so 53 stands and the term after it is the one to replace.

Common traps

• Blaming 53 because the gap after it is off, when the gap into it (16) fits
• Picking the first term that looks large without checking every gap against the rule

No directly related past PYQ was found.