64.6+81.4+17.6

=6.(64+17)+81.4

=6.81+81.4

=81.(6+4)

=81.10

=810

g) Ta có: \(64\cdot6+81\cdot4+17\cdot6\)

\(=6\left(64+17\right)+81\cdot4\)

\(=81\cdot6+81\cdot4\)

=810

64.6+81.4+17.6

=6.(64+17)+81.4

=6.81+81.4

=81.(6+4)

=81.10

=810

12 . 19 + 12

= 12 . 19 + 12 . 1

= 12 . ( 19 + 1 )

= 12 . 20

= 240

\(12\cdot19+12=12\left(19+1\right)=12\cdot20=240\)

\(A=\dfrac{3}{7x10}+\dfrac{3}{10x13}+\dfrac{3}{13x16}+...+\dfrac{3}{97x100}\)

\(A=3x\left(\dfrac{1}{7x10}+\dfrac{1}{10x13}+\dfrac{1}{13x16}+...+\dfrac{1}{97x100}\right)\)

\(A=3x\dfrac{1}{3}x\left(\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{16}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\)

\(A=3x\dfrac{1}{3}x\left(\dfrac{1}{7}-\dfrac{1}{100}\right)\)

\(A=1x\left(\dfrac{100}{700}-\dfrac{7}{700}\right)=\dfrac{93}{700}\)

\(365365\div\left(91\times55\right)\)

=365365\(\div\) 5005

=73

`125+231+319+769+875+681`

`= (125+875) + ( 231+769) + ( 319+681 ) `

`= 1000 + 1000 + 1000 `

`= 3000`

TL:

(93273+398)+(727+5602)= 93671+ 6329

=100000

-HT-

  93273+398+727+5602 = (   93273 +  727 ) + ( 5602  + 398 ) 

= 94000 + 6000 

= 100000

Thuận hợp lí???

1/2:2/4.3/5

=1.3/5

=3/5

\(\dfrac{1}{2}\times\dfrac{3}{5}:\dfrac{2}{4}=\dfrac{1}{2}\times\dfrac{3}{5}\times2=\left(\dfrac{1}{2}\times2\right)\times\dfrac{3}{5}=1\times\dfrac{3}{5}=\dfrac{3}{5}\)