In each of these questions a number series is given. In each series only one…

Concept

In an alternating number series, two operations act in turn on consecutive terms. Here each step alternates between subtraction and addition, and the magnitude of the change grows by 11 every step: subtract 11, add 22, subtract 33, add 44, subtract 55, add 66. The one term that does not result from this fixed rule is the wrong number.

Application

Apply the rule to 188 step by step and compare each result with the given term:

1. 188 − 11 = 177 (matches the given 177)

2. 177 + 22 = 199 (matches the given 199)

3. 199 − 33 = 166 (matches the given 166)

4. 166 + 44 = 210 (matches the given 210)

5. 210 − 55 = 155 (the given term here is 150, not 155 — this is the break)

6. 155 + 66 = 221 (matches the given 221, confirming 155 is the intended value at the previous step)

Every step obeys the rule except the sixth term, where the series shows 150 instead of the required 155.

Cross-check

Read the series as two interleaved chains. The terms in the 1st, 3rd, 5th and 7th places are 188, 199, 210, 221 — a clean +11 chain. The terms in the 2nd, 4th and 6th places should be 177, 166, 155 — a clean −11 chain — but the series gives 177, 166, 150. The 150 again breaks the −11 chain, so 150 is the wrong number and should be 155.