Câu 2: Trang 53 sách VNEN toán 4
Rút gọn rồi tính:
$\frac{3}{9}\times \frac{5}{4}$
$\frac{7}{3}\times \frac{2}{8}$
$\frac{12}{15}\times \frac{12}{9}$
Bài Làm:
$\frac{3}{9}\times \frac{5}{4}$
- $\frac{3}{9}=\frac{3:3}{9:3}=\frac{1}{3}$
- $\frac{1}{3}\times \frac{5}{4}=\frac{1\times 5}{3\times 4}=\frac{5}{12}$
$\frac{7}{3}\times \frac{2}{8}$
- $\frac{2}{8}=\frac{2:2}{8:2}=\frac{1}{4}$
- $\frac{7}{3}\times \frac{1}{4}=\frac{7\times 1}{3\times 4}=\frac{7}{4}$
$\frac{12}{15}\times \frac{12}{9}$
- $\frac{12}{15}=\frac{12:3}{15:3}=\frac{4}{5}$
- $\frac{12}{9}=\frac{12:3}{9:3}=\frac{4}{3}$
- $\frac{4}{5}\times \frac{4}{3}=\frac{4\times 4}{5\times 3}=\frac{16}{15}$