a ) 5/11.5/7+5/11.2/7+6/11 b ) 3/13.6/11+3/13.9/11-3/13.4/11

Đáp án:

 `a)` `5/11 . 5/7 + 5/11 . 2/7 + 6/11`

  `= 5/11 . ( 5/7 + 2/7 ) + 6/11`

  `= 5/11 . 1 + 6/11`

  `= 5/11 + 6/11`
 
  `= 1`

 `b)` `3/13 . 6/11 + 3/13 . 9/11 - 3/13 . 4/11`
  
  `= 3/13 . (6/11 + 9/11 - 4/11)`

  `= 3/13 . 11/11`

  `= 3/13 . 1`

  `= 3/13`

Giải thích các bước giải:

$\text{Đáp án+Giải thích các bước giải:}$

$\text{Câu A:}$

$\dfrac{5}{11}$×$\dfrac{5}{7}$+$\dfrac{5}{11}$×$\dfrac{2}{7}$+$\dfrac{6}{11}$

=($\dfrac{5}{11}$×$\dfrac{5}{7}$)+($\dfrac{5}{11}$×$\dfrac{2}{7}$)+$\dfrac{6}{11}$

=$\dfrac{25}{77}$+$\dfrac{10}{77}$+$\dfrac{6}{11}$

=$\dfrac{25×1}{77}$+$\dfrac{10×1}{77}$+$\dfrac{6×7}{77}$

=$\dfrac{25+10+42}{77}$

=$\dfrac{77}{77}$

= 1

$\text{Câu B:}$

$\dfrac{3}{13}$×$\dfrac{6}{11}$+$\dfrac{3}{13}$×$\dfrac{9}{11}$-$\dfrac{3}{13}$×$\dfrac{4}{11}$

=($\dfrac{3}{13}$×$\dfrac{6}{11}$)+($\dfrac{3}{13}$×$\dfrac{9}{11}$)-($\dfrac{3}{13}$×$\dfrac{4}{11}$)

=$\dfrac{18}{143}$+$\dfrac{27}{143}$-$\dfrac{12}{143}$

=$\dfrac{18+27-12}{143}$

=$\dfrac{33}{143}$

=$\dfrac{3}{13}$