a) Hình 1: $\frac{3}{7}$ ; Hình 2: $\frac{3}{8}$ ; Hình 3: $2\frac{1}{4}$
b)
c) Lỗi sai: $\frac{3}{4} = \frac{{12}}{{20}}$ ; Sửa lại: $\frac{3}{4} = \frac{{3 \times 5}}{{4 \times 5}} = \frac{{15}}{{20}}$
Lỗi sai: $\frac{3}{5} = \frac{{12}}{{30}}$ ; Sửa lại: $\frac{3}{5} = \frac{{3 \times 6}}{{5 \times 6}} = \frac{{18}}{{30}}$
Lỗi sai: $\frac{1}{6} = \frac{6}{{54}}$ ; Sửa lại: $\frac{1}{6} = \frac{{1 \times 9}}{{6 \times 9}} = \frac{9}{{54}}$
d) $\frac{5}{8} + \frac{1}{3} = \frac{{15}}{{24}} + \frac{8}{{24}} = \frac{{23}}{{24}}$
$\frac{1}{6} + \frac{8}{9} = \frac{3}{{18}} + \frac{{16}}{{18}} = \frac{{19}}{{18}}$
$\frac{4}{5} - \frac{3}{4} = \frac{{16}}{{20}} - \frac{{15}}{{20}} = \frac{1}{{20}}$
$\frac{5}{{12}} - \frac{3}{{20}} = \frac{{25}}{{60}} - \frac{9}{{60}} = \frac{{16}}{{60}} = \frac{4}{{15}}$