4) (13×5) × 2 = 13 × (5 × 2) = 13 × 10 = 1305) (7 × 2) × 50 = 7 × (2 × 50) = 7 × 100 = 7006) (18 × 25) × 4 = 18 × (25 × 4) = 18 × 100 = 1800
4) (13×5) × 2 = 13 × (5 × 2) = 13 × 10 = 130
5) (7 × 2) × 50 = 7 × (2 × 50) = 7 × 100 = 700
6) (18 × 25) × 4 = 18 × (25 × 4) = 18 × 100 = 1800