Giải bài tập 4 trang 66 vbt Toán 4 tập 2 Cánh diều

a) 

$(\frac{1}{4}\times \frac{2}{3})\times \frac{3}{5}=\frac{2}{12}\times \frac{3}{5}=\frac{1}{6}\times \frac{3}{5}=\frac{3}{30}=\frac{1}{10}$

$\frac{1}{4}\times (\frac{2}{3}\times \frac{3}{5})=\frac{1}{4}\times \frac{2}{5}=\frac{2}{20}=\frac{1}{10}$

Vậy $(\frac{1}{4}\times \frac{2}{3})\times \frac{3}{5}$ = $\frac{1}{4}\times (\frac{2}{3}\times \frac{3}{5})$.

$(\frac{1}{2}\times \frac{1}{6})\times \frac{1}{5}=\frac{1}{12}\times \frac{1}{5}=\frac{1}{60}$

$\frac{1}{2}\times (\frac{1}{5}\times \frac{1}{6})=\frac{1}{2}\times \frac{1}{30}=\frac{1}{60}$

Vậy $(\frac{1}{2}\times \frac{1}{6})\times \frac{1}{5}$ = $\frac{1}{2}\times (\frac{1}{5}\times \frac{1}{6})$.

b) Ví dụ:

$(\frac{1}{3}\times \frac{2}{3})\times \frac{4}{5}=\frac{2}{9}\times \frac{4}{5}=\frac{8}{45}$

$\frac{1}{3}\times (\frac{2}{3}\times \frac{4}{5})=\frac{1}{3}\times \frac{8}{15}=\frac{8}{45}$

Vậy $(\frac{1}{3}\times \frac{2}{3})\times \frac{4}{5}$ = $\frac{1}{3}\times (\frac{2}{3}\times \frac{4}{5})$.