A group of 630 children seated in rows for a group photo session. Each row contains three less children than the row in front of it. Which one of the following number of rows is not possible?

Explanation

Official WBPSC key (Series A): (D) 6. The rows form an arithmetic progression with common difference −3 totalling 630: 3 rows → first row 213 (possible); 4 rows → 162 (possible); 5 rows → 132 (possible); 6 rows → 112.5, not an integer (not possible).