Boys = 7 units, girls = 8 units. The 7 units of boys are 42, so each unit is 6.

Boys6666666Girls66666666

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

  1. Boys → 7 units = 42
  2. 1 unit → 42 ÷ 7 = 6
  3. Girls → 8 units = 8 × 6 = 48

There are 48 girls.

Check: 42 : 48 = 7 : 8. ✓