Toán Lớp 4: 1.Tính nhanh : 326 x 78 + 327 x 22 4 x 113 x 25 – 5 x 112 x 20 2. Tính nhanh:
a, 237 + 357 + 763 b, 2345 + 4257 – 345 c, 4276 + 2357 + 5724 + 7643 d, 3145 + 2496 + 5347 + 7504 + 4653 e, 2376 + 3425 – 376 – 425 g, 3145 – 246 + 2347 – 145 + 4246 – 347
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= 326 × 78 + (326 + 1) × 22
= 326 × 78 + 326 × 22 + 1 × 22
= 326 × (78 + 22) + 22
= 326 × 100 + 22
= 32600 + 22
= 32622 4 x 113 × 25 – 5 × 112 × 20
= 4 x 25 × 113 – 5 x 20 × 112
= 100 × 113 – 100 × 112
= 100 × ( 113 – 112)
= 100 × 1
= 100
b, 2345 + 4257 – 345
c, 4276 + 2357 + 5724 + 7643
d, 3145 + 2496 + 5347 + 7504 + 4653
= 3145 + ( 2496 + 7504 ) + ( 5347 + 4653 )
= 3145 + 10000 + 10000
= 3145 + 20000
e, 2376 + 3425 – 376 – 425
= ( 2376 – 376 ) + ( 3425 – 425 )
= 2000 + 3000
g, 3145 – 246 + 2347 – 145 + 4246 – 347
= ( 3145 – 145 ) + ( 4246 – 246 ) + ( 2347 – 347 )
= 3000 + 4000 + 2000
= 326 x 78 + 326 x 22 + 1 x 22
= 326 x (78 + 22) + 22
= 326 x 100 + 22
= 32600 + 22
= 32622
= 4 x 25 x 113 – 5 x 20 x 112
= 100 x 113 – 100 x 112
= 100 x ( 113 – 112)
= 100 x 1
= 100
b, 2345 + 4257 – 345 = (2345 – 345) + 4257 = 2000 + 4257 = 6257
c, 4276 + 2357 + 5724 + 7643 = (4276 + 5724) + (2357 + 7643) = 10000 + 10000 = 20000
d, 3145 + 2496 + 5347 + 7504 + 4653
= 3145 + (2496 + 7504) + (5347 + 4653)
= 3145 + 10000 + 10000
= 3145 + 20000 = 23145
e, 2376 + 3425 – 376 – 425
= (2376 – 376) + (3425 – 425)
= 2000 + 3000 = 5000
g, 3145 – 246 + 2347 – 145 + 4246 – 347
= (3145 – 145) + (4246 – 246) + (2347 – 347)
= 3000 + 4000 + 2000 = 9000