Thực hiện phép tính a) 15/34 + 7/21 + 19/34 - 20/15 + 3/7 b) 26 (1/5)* 3/4 - 3/4* 44(1/5)

* Hướng dẫn giải

a) $\frac{15}{34}+\frac{7}{21}+\frac{19}{34}-\frac{20}{15}+\frac{3}{7}$ 

$=\left(\frac{15}{34}+\frac{19}{34}\right)+\left(\frac{7}{21}-\frac{20}{15}\right)+\frac{3}{7}$ 

$=\frac{15+19}{34}+\left(\frac{7:7}{21:7}-\frac{20:5}{15:5}\right)+\frac{3}{7}$ 

$=\frac{34}{34}+\left(\frac{1}{3}-\frac{4}{3}\right)+\frac{3}{7}$ 

$=1+\frac{-3}{3}+\frac{3}{7}=1+(-1)+\frac{3}{7}=\frac{3}{7}$ 

b) $26\frac{1}{5}.\frac{3}{4}-\frac{3}{4}.44\frac{1}{5}$ 

$=\frac{3}{4}\left(26\frac{1}{5}-44\frac{1}{5}\right)$ 

$=\frac{3}{4}.\left(\frac{26.5+1}{5}-\frac{44.5+1}{5}\right)$ 

$=\frac{3}{4}.\left(\frac{131}{5}-\frac{221}{5}\right)$ 

$=\frac{3}{4}.\frac{131-221}{5}$ 

$=\frac{3}{4}.\frac{-90}{5}=\frac{3.(-90)}{4.5}$ 

$=\frac{\mathrm{3.5.2.}(-9)}{\mathrm{2.2.5}}=\frac{-27}{2}$