Find wrong number in series: 15, 25, 30, 51, 85, 90, 115

Concept

In a “find the wrong number in the series” question, most terms follow one common numerical rule (a fixed common difference, ratio, or divisibility rule); the single term that breaks that rule is the wrong number.

Application

1. 15 ÷ 5 = 3 — divisible by 5

2. 25 ÷ 5 = 5 — divisible by 5

3. 30 ÷ 5 = 6 — divisible by 5

4. 51 ÷ 5 = 10.2 — NOT divisible by 5

5. 85 ÷ 5 = 17 — divisible by 5

6. 90 ÷ 5 = 18 — divisible by 5

7. 115 ÷ 5 = 23 — divisible by 5

Cross-check

Every multiple of 5 ends in the digit 0 or 5. Six of the seven terms end in 0 or 5; 51 ends in 1, independently confirming that it alone breaks the pattern.

Answer

51 is the wrong number in the series.