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

Concept

In a 'find the wrong number' series, first identify the single rule that links each term to the next (a constant ratio, a constant difference, or a fixed operation). Once the rule is fixed, the one term that violates it is the wrong number.

Application

Test the ratio between consecutive terms from the left:

1. 18225 ÷ 3 = 6075 — holds

2. 6075 ÷ 3 = 2025 — holds

3. 2025 ÷ 3 = 675 — holds

4. 675 ÷ 3 = 225, but the series shows 220 — breaks the rule

5. 225 ÷ 3 = 75 — holds

6. 75 ÷ 3 = 25 — holds

The governing rule is 'divide the previous term by 3.' Every step obeys it except the fifth term, where the value should be 225 but appears as 220.

Cross-check

Replace 220 with 225 and read the corrected series: 18225, 6075, 2025, 675, 225, 75, 25. Now 225 ÷ 3 = 75 and 75 ÷ 3 = 25, so every consecutive pair has the exact ratio 3. This confirms 220 is the only term that does not fit, so 220 is the wrong number.