Tính: 2/3 + 5/2 - 3/4

Giải Toán lớp 4 Bài: Ôn tập về các phép tính với phân số (tiếp theo)

Toán lớp 4 trang 170 Bài 3:

a)

$\frac{2}{3}+\frac{5}{2}-\frac{3}{4}\frac{2}{5}\times \frac{1}{2}:\frac{1}{3}\frac{2}{9}:\frac{2}{9}\times \frac{1}{2}$                                                                         

b)  

$\frac{4}{5}-\frac{1}{2}+\frac{1}{3}\frac{1}{2}\times \frac{1}{3}+\frac{1}{4}\frac{2}{7}:\frac{2}{3}-\frac{1}{7}$                                                                       

Lời giải

a)

$\frac{2}{3}+\frac{5}{2}-\frac{3}{4}=\frac{8}{12}+\frac{30}{12}-\frac{9}{12}$$=\frac{38}{12}-\frac{9}{12}=\frac{29}{12}$

$\frac{2}{5}\times \frac{1}{2}:\frac{1}{3}=\frac{2\times 1}{5\times 2}\times \frac{3}{1}=\frac{\cancel{2}\times 1\times 3}{5\times \cancel{2}\times 1}=\frac{3}{5}$

$\frac{2}{9}:\frac{2}{9}\times \frac{1}{2}=1\times \frac{1}{2}=\frac{1}{2}$

b)

$\frac{4}{5}-\frac{1}{2}+\frac{1}{3}=\frac{24}{30}-\frac{15}{30}+\frac{10}{30}$$=\frac{9}{30}+\frac{10}{30}=\frac{19}{30}$

$\frac{1}{2}\times \frac{1}{3}+\frac{1}{4}=\frac{1}{6}+\frac{1}{4}=\frac{2}{12}+\frac{3}{12}=\frac{5}{12}$

$\frac{2}{7}:\frac{2}{3}-\frac{1}{7}=\frac{2}{7}\times \frac{3}{2}-\frac{1}{7}=\frac{3}{7}-\frac{1}{7}=\frac{2}{7}$