Giải bài 39 trang 40

Đề bài

Thực hiện các phép tính sau:

a) $\frac{5}{12}+\frac{21}{8}.\frac{1}{14}$

b) $\frac{8}{15}.\frac{3}{64}-\frac{13}{25}.$

c) $\left(\frac{19}{21}-\frac{2}{3}\right).\frac{28}{10}$

d) $\left(1-\frac{5}{17}\right).\left(\frac{3}{8}-\frac{5^2}{24}\right)$

Lời giải chi tiết

a) $\frac{5}{12}+\frac{21}{8}.\frac{1}{14}=\frac{5}{12}+\frac{3}{16}=\frac{20}{48}+\frac{9}{48}=\frac{29}{48}$

b) $\frac{8}{15}.\frac{3}{64}-\frac{13}{25}=\frac{8.3}{15.64}-\frac{13}{25}=\frac{1}{40}-\frac{13}{25}=\frac{5}{200}-\frac{104}{200}=\frac{-99}{200}$

c) $\left(\frac{19}{21}-\frac{2}{3}\right).\frac{28}{10}=\left(\frac{19}{21}-\frac{14}{21}\right).\frac{28}{10}=\frac{5}{21}.\frac{14}{5}=\frac{2}{3}$

d) $\left(1-\frac{5}{17}\right).\left(\frac{3}{8}-\frac{5^2}{24}\right)=\left(\frac{17}{17}-\frac{5}{17}\right).\left(\frac{9}{24}-\frac{25}{24}\right)=\frac{12}{17}.\frac{-16}{24}=\frac{-8}{17}$