Find out the WRONG number in the given series. 336, 246, 166, 94, 36, −14

Correct — A.
Rule: the differences fall by 10: −90, −80, −70, −60, −50.

336 − 90 = 246, fits.
246 − 80 = 166, fits.
166 − 70 = 96, but the series prints 94.
96 − 60 = 36 and 36 − 50 = −14, both fit.

94 is the wrong number → option (a).

Why the others are wrong

• (b)
  166 — 166 fits: 246 − 80 = 166 is the second step of the rule. The break comes one step later, where 166 − 70 should give 96.
• (c)
  246 — 246 is the first step of the rule, 336 − 90 = 246, and the step after it, 246 − 80 = 166, fits too.
• (d)
  36 — 36 only looks wrong because 94 − 36 = 58. Put 96 in place of 94 and both 96 − 60 = 36 and 36 − 50 = −14 fit.

In a wrong-number series, write the differences first. One wrong term spoils two neighbouring differences, the one into it and the one out of it.

Here the differences read 90, 80, 72, 58, 50. The two odd ones sit on either side of 94. Replace 94 with 96 and they become 70 and 60, completing the steady fall by 10.

Key facts

• A single wrong term disturbs the difference before it and the difference after it.
• Here the differences should run 90, 80, 70, 60, 50, falling by 10 each time.
• The term that belongs in place of 94 is 96.

Common traps

• Blaming 166 because the first uneven difference, 72, starts from it
• Blaming 36 because 94 − 36 = 58 also looks wrong

No directly related past PYQ was found.