Failed = 25% = 1 unit; passed = 75% = 3 units, so the whole class is 4 units. The 16 extra pupils make up 2 units.

Failed1Passed11116 more = 2 units

Plain numbers are given; italic underlined numbers are worked out.

  1. Passed − failed → 2 units → 16
  2. 1 unit → 16 ÷ 2 = 8
  3. Whole class → 4 units = 4 × 8 = 32

There are 32 pupils in the class.

Check: failed 8 + passed 24 = 32; 8 is 25% of 32. ✓