Question

10．计算

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 除以一个分数，等于乘这个分数的倒数；分数乘整数或分数，首先分子或整数与分母约分，然后分子或分母分别相乘；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$\frac{2}{3}$

点评 此题考查了分数的乘法和除法运算，要首先除法化成乘法，再约分，然后分子分母分别相乘．