Bài 1 tính a. (-3/7 + 2/5) - 9/70 b. 2 + 4/5 - 7/12 c.3/7 × 9/26 - 3/7

Đáp án+Giải thích các bước giải:

Bài 1: tính

 a) $(-\dfrac{3}{7}$ + $\dfrac{2}{5})$  - $\dfrac{9}{70}$

= $\dfrac{-3}{7}$ + $\dfrac{2}{5}$ - $\dfrac{9}{70}$

= $\dfrac{-30}{70}$ + $\dfrac{28}{70}$ - $\dfrac{9}{70}$

= $\dfrac{-30 + 28 - 9}{70}$

= $\dfrac{-11}{70}$

b) 2 + $\dfrac{4}{5}$ - $\dfrac{7}{12}$

= $\dfrac{120}{60}$ + $\dfrac{48}{60}$ - $\dfrac{35}{60}$

= $\dfrac{120 + 48 - 35}{60}$

=   $\dfrac{133}{60}$

c) $\dfrac{3}{7}$ x $\dfrac{9}{26}$ - $\dfrac{3}{7}$

= $\dfrac{3 .9}{7 .26}$ - $\dfrac{3}{7}$

= $\dfrac{27}{182}$ - $\dfrac{3}{7}$

= $\dfrac{27}{182}$ - $\dfrac{78}{182}$

= $\dfrac{27 - 78}{182}$

= $\dfrac{-51}{182}$