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a) 1268 + 99 + 501= 1268 + ( 99 + 501)
…= 1268 + 600 = 1868
745 + 268 + 732= 745 + ( 268 + 732 )
= 745 + 1000 = 1745
1295 +105 + 1460= 1400 + 1460
= 2860
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,142\times12+142\times18=142\times\left(12+18\right)=142\times30=4260\\ b,49\times365-39\times365=365\times\left(49-39\right)=365\times10=3965\\ c,4\times18\times25=\left(4\times25\right)\times18=100\times18=1800\)
a) 142 x 12 + 142 x 18
=142x(12+18)
=142x30
=4260
b) 49 x 365 - 39 x 365
=(49-39)x365
=10x365
=3650
c) 4 x 18 x 25
=4x25x18
=100x18
=1800
![](https://rs.olm.vn/images/avt/0.png?1311)
325 + 1268 + 332 + 675
= (325 + 675) + (1268 + 332)
= 1000 + 1600
= 2600
HT
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a, 2 x 9 x 5 x 7 x 4 x 25
= 23 x 32 x 53 x 7
= 63000
b, 6 x 14 x 5 x 25 x 3 x 4
= 24 x 32 x 53 x 7
= 126000
a) 2x9x5x7x4x25
= (2x5)x(4x25)x(9x7)
= 10x100x63
= 63000
b) 2x14x5x25x3x4
= (2x5)x(4x25)x(14x3)
= 10x100x42
= 42000
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\left(81+19\right)+35=135\)
b) \(\left(78+22\right)+\left(65+135\right)=100+200=300\)
c) \(\left(234+17716\right)+23=17950+23=17973\)
d) \(\left(99+1\right)+85=100+85=185\)
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a) \(\dfrac{3}{5}\times\dfrac{17}{21}+\dfrac{17}{21}\times\dfrac{2}{5}\)
\(=\dfrac{17}{21}\times\left(\dfrac{3}{5}+\dfrac{2}{5}\right)\)
\(=\dfrac{17}{21}\times1\)
\(=\dfrac{17}{21}\)
b) \(\dfrac{15}{8}:\dfrac{5}{20}-\dfrac{7}{8}:\dfrac{1}{4}\)
\(=\dfrac{15}{8}\times\dfrac{20}{5}-\dfrac{7}{8}\times4\)
\(=\dfrac{15}{8}\times4-\dfrac{7}{8}\times4\)
\(=4\times\left(\dfrac{15}{8}-\dfrac{7}{8}\right)\)
\(=4\times1\)
\(=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 35 x 2 x 9 x 5
= (35 x 9) x (2 x 5)
= (35 x 10 - 35) x 10
= (350 - 35) x 10
= 315 x 10 = 3150
b) 24 x 71 + 71 x 75 + 71
= 71 x (24+75+1)
=71 x 100
= 7100
a) 1268 + 99 + 501 = 1868
b) 138 + 645 + 862 = 1645
c) 131 + 85 + 469 = 685
a 1268+99+501
=1268+[99+501]
=1268+600
=1868
b138+645+862
=[138+862]+645
=1000+645
=1645
c 131+85+469
=[131+469]+85
=600+85
=685