Question

Tính bằng cách thuận tiện nhất 12/13 x 2/5 + 4/5 x 4/13 + 8/26 + 3 : 13/4

Answer 1

\(\dfrac{12}{13}\times\dfrac{2}{5}+\dfrac{4}{5}\times\dfrac{4}{13}+\dfrac{8}{26}+3:\dfrac{13}{4}\\ =\dfrac{4}{13}\times3\times\dfrac{2}{5}+\dfrac{4}{5}\times\dfrac{4}{13}+\dfrac{4}{13}\times\dfrac{2}{2}+3\times\dfrac{4}{13}\\ =\dfrac{4}{13}\times\dfrac{6}{5}+\dfrac{4}{5}\times\dfrac{4}{13}+\dfrac{4}{13}\times1+3\times\dfrac{4}{13}\\ =\dfrac{4}{13}\times\left(\dfrac{6}{5}+\dfrac{4}{5}+1+3\right)\\ =\dfrac{4}{13}\times6\\ =\dfrac{24}{13}\)

Answer 2

`12/13 xx 2/5 + 4/5 xx 4/13 + 8/26 + 3 : 13/4`

`= 12/13 xx 2/5 + 4/5  xx 4/13 + 4/13 xx 1 + 3 xx 4/13`

`= 4/13 xx 3 xx 2/5 + 4/5 xx 4/13 + 4/13 xx 1  + 3 xx 4/13`

`= 4/13 xx 6/5 + 4/5 xx 4/13 + 4/13 xx 1 + 3 xx 4/13`

`= 4/13 xx (6/5 + 4/5 + 1 + 3)`

`= 4/13 xx ( 2 + 1 + 3)`

`= 4/13 xx ( 3 + 3)`

`= 4/13 xx 6`

`= (4 xx 6)/13`

`= 24/13`

_______________________________________________

`a xx b + c xx b + b`

`= a xx b + c xx b + b xx 1`

`= b xx (a + c + 1)`