Tính bằng cách thuận tiện. a) 349 + 602 + 651 + 398

a) 349 + 602 + 651 + 398

= (346 + 651) + (602 + 398)

= 1000 + 1000

= 2000

b) 19 × 82 + 18 × 19

= 19 × (82 + 18)

= 19 × 100

= 1900

c) 35 × 18 – 9 × 70 + 100

= 35 × 2 × 9 – 9 × 70 + 100

= 70 × 9 – 9 × 70 + 100

= 0 + 100

= 100

d) 4 × 125 × 25 × 8

= (4 × 25) × (8 × 125)

= 100 × 1000

= 100 000

e) 3145 – 246 + 2 347 – 145 + 4 246 – 347

= (3 145 – 145) + (4 246 – 246) + (2 347 – 347)

= 3000 + 4000 + 2000

= 7000 + 2000

= 9000

f) 325 × 1 574 – 325 × 325 – 325 × 249

= 325 × (1 574 – 325 – 249)

= 325 × 1000

= 325 000

g) 326 × 78 + 327 × 22

= 326 × 78 + (326 + 1) × 22

= 326 × 78 + 326 × 22 + 1 × 22

= 326 × (78 + 22) + 22

= 326 × 100 + 22

= 32 600 + 22

= 32 622

h) 2 × 8 × 50 × 25 × 125

= (2 × 50) × (125 × 8) × 25

= 100 × 1000 × 25

= 2 500 000