Question

10．計算

①$\frac{15}{39}$×26	②$\frac{38}{45}$×$\frac{10}{19}$	③$\frac{28}{15}$×$\frac{10}{21}$
④$\frac{2}{3}$×6÷$\frac{3}{8}$	⑤$\frac{5}{9}$×$\frac{2}{7}$×$\frac{7}{10}$	⑥$\frac{4}{21}$×28÷$\frac{4}{5}$

Answer 1

分析 除以一個分數(shù)，等于乘這個分數(shù)的倒數(shù)；分數(shù)乘整數(shù)或分數(shù)，首先分子或整數(shù)與分母約分，然后分子或分母分別相乘；即可得解．

解答 解：①$\frac{15}{39}$×26=10

②$\frac{38}{45}$×$\frac{10}{19}$=$\frac{4}{5}$

③$\frac{28}{15}$×$\frac{10}{21}$=$\frac{8}{9}$

④$\frac{2}{3}$×6÷$\frac{3}{8}$ 
=$\frac{2}{3}$×6×$\frac{8}{3}$
=10$\frac{2}{3}$

⑤$\frac{5}{9}$×$\frac{2}{7}$×$\frac{7}{10}$=$\frac{1}{9}$

⑥$\frac{4}{21}$×28÷$\frac{4}{5}$
=$\frac{4}{21}$×28×$\frac{5}{4}$
=$\frac{20}{3}$
=6$\frac{2}{3}$

點評 此題考查了分數(shù)的乘法和除法運算，要首先除法化成乘法，再約分，然后分子分母分別相乘．