a) 2 × 76 × 500

b) 5 × 300 × 800

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c) 70 × 21 + 30 × 21

d) 81 × 28 – 81 × 18

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a) 2 × 76 × 500

= (2 × 500) × 76

= 1 000 × 76

= 76 000

b) 5 × 300 × 800

= (5 × 800) × 300

= 4 000 × 300

= 1 200 000

c) 70 × 21 + 30 × 21

= 21 × (70 + 30)

= 21 × 100

= 2 100

d) 81 × 28 – 81 × 18

= 81 × (28 – 18)

= 81 × 10

= 810