Tính (theo mẫu): 9/10*5/6

Giải Toán lớp 5 Ôn tập: Phép nhân và phép chia hai phân số

Toán lớp 5 trang 11 Bài 2:

a)$\frac{9}{10}\times \frac{5}{6}$               

b)$\frac{6}{25}:\frac{21}{20}$                       

c)$\frac{40}{7}\times \frac{14}{5}$                       

d)$\frac{17}{13}:\frac{51}{26}$

Mẫu: a)$\frac{9}{10}\times \frac{5}{6}=\frac{9\times 5}{10\times 6}$

$=\frac{\cancel{3}\times 3\times \cancel{5}}{\cancel{5}\times 2\times \cancel{3}\times 2}=\frac{3}{4}$

Lời giải

a)$\frac{9}{10}\times \frac{5}{6}=\frac{9\times 5}{10\times 6}$

$=\frac{\cancel{3}\times 3\times \cancel{5}}{\cancel{5}\times 2\times \cancel{3}\times 2}=\frac{3}{4}$

b)$\frac{6}{25}:\frac{21}{20}=\frac{6}{25}\times \frac{20}{21}$

$=\frac{6\times 20}{25\times 21}=\frac{\bcancel{3}\times 2\times 4\times \bcancel{5}}{\bcancel{5}\times 5\times \bcancel{3}\times 7}$

$=\frac{8}{35}$

c)$\frac{40}{7}\times \frac{14}{5}=\frac{40\times 14}{7\times 5}$

$=\frac{\bcancel{5}\times 8\times \bcancel{7}\times 2}{\bcancel{7}\times \bcancel{5}}=16$                 

d)$\frac{17}{13}:\frac{51}{26}=\frac{17}{13}\times \frac{26}{51}$

$=\frac{17\times 26}{13\times 51}=\frac{\cancel{17}\times \cancel{13}\times 2}{\cancel{13}\times \cancel{17}\times 3}$

$=\frac{2}{3}$