Bài 2 trang 11 sgk toán 5


Bài 2. Tính:

Bài 2. Tính:

a) \( \frac{9}{10}.\frac{5}{6}\) ;   b) \( \frac{6}{25}:\frac{21}{20}\) ;    c) \( \frac{40}{7}.\frac{14}{5}\) ;    d) \( \frac{17}{13}:\frac{51}{26}\) .

Bài giải:

a) \( \frac{9}{10}.\frac{5}{6}\) \( = \frac{9.5}{10.6}=\frac{3.3.5}{2.5.2.3}=\frac{3}{4}\) ;

b) \( \frac{6}{25}:\frac{21}{20}\) \( = \frac{6}{25}.\frac{20}{21}=\frac{3.2.4.5}{5.5.7.3}=\frac{8}{35}\) ;

c) \( \frac{40}{7}.\frac{14}{5}\) \( =\frac{40.14}{7.5}=\frac{4.5.2.2.7}{5.7}=16\) ;

d) \( \frac{17}{13}:\frac{51}{26}\) \( \frac{17}{13}.\frac{26}{51}=\frac{17.2.13}{13.3.17}=\frac{2}{3}\) .