Take the 35 adults out of the 200 first. That leaves boys + girls; girls = 1 unit, boys = 2 units.

Girls1Boys11Adults35200

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

  1. Boys + Girls → 200 − 35 = 165
  2. 3 units → 165
  3. 1 unit (girls) → 165 ÷ 3 = 55
  4. Boys = 2 units → 2 × 55 = 110

There are 110 boys.

Check: girls 55 + boys 110 + adults 35 = 200. ✓