Total push-ups for 4 boys = 38 × 4 = 152.
Total push-ups for Bobby, Simon & Gilbert = 37 × 3 = 111.
• Kok Hong = Total (4 boys) − Total (3 boys)
• Kok Hong = 152 − 111 = 41 push-ups
Kok Hong did 41 push-ups.
Check: (B+S+G = 111, K=41). Average of all 4 = (111+41)÷4 = 38. ✓