Question

Bài tập : tính nhanh

2/9+3/7+15/13+4/7-2/13+7/9

=...............................................

Answer 1

\(\dfrac{2}{9}+\dfrac{3}{7}+\dfrac{15}{13}+\dfrac{4}{7}-\dfrac{2}{13}+\dfrac{7}{9}\)

\(=\left(\dfrac{2}{9}+\dfrac{7}{9}\right)+\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\left(\dfrac{15}{13}-\dfrac{2}{13}\right)\)

\(=\dfrac{9}{9}+\dfrac{7}{7}+\dfrac{13}{13}=1+1+1=3\)

Answer 2

`2/9+3/7+15/13+4/7-2/13+7/9`

 

`= (2/9 + 7/9 ) + ( 3/7 + 4/7 ) + ( 15/13-2/13 ) `

 

`= 9/9 + 7/7 + 13/13`

 

`=   1 + 1 + 1 = 3`