Tính bằng cách hợp lý nhất :
a]3.26x728+3.26+3.26x270
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g) Ta có: \(64\cdot6+81\cdot4+17\cdot6\)
\(=6\left(64+17\right)+81\cdot4\)
\(=81\cdot6+81\cdot4\)
=810
\(A=\dfrac{3}{7x10}+\dfrac{3}{10x13}+\dfrac{3}{13x16}+...+\dfrac{3}{97x100}\)
\(A=3x\left(\dfrac{1}{7x10}+\dfrac{1}{10x13}+\dfrac{1}{13x16}+...+\dfrac{1}{97x100}\right)\)
\(A=3x\dfrac{1}{3}x\left(\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{16}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\)
\(A=3x\dfrac{1}{3}x\left(\dfrac{1}{7}-\dfrac{1}{100}\right)\)
\(A=1x\left(\dfrac{100}{700}-\dfrac{7}{700}\right)=\dfrac{93}{700}\)
\(365365\div\left(91\times55\right)\)
=365365\(\div\) 5005
=73
`125+231+319+769+875+681`
`= (125+875) + ( 231+769) + ( 319+681 ) `
`= 1000 + 1000 + 1000 `
`= 3000`
125+231+319+769+875+681
=(125+875)+(231+769)+(319+681)
=1000+1000+1000
=3000
93273+398+727+5602 = ( 93273 + 727 ) + ( 5602 + 398 )
= 94000 + 6000
= 100000
=3,26(728+1+270)
=3,26*999=3256,74
\(3,26\cdot728+3,26+3,26\cdot270\)
\(=3,26\cdot\left(728+1+270\right)\)
\(=3,26\cdot999\)
\(=3,26\cdot\left(1000-1\right)\)
\(=3,26\cdot1000-1\cdot3,26\)
\(=3260-3,26\)
\(=3256,74\)