II. Phần tự luận. (7 điểm)

Tính rồi rút gọn:

\(\frac{{13}}{{40}} + \frac{{17}}{{40}} = \)…………………………                   \(\frac{{17}}{{20}} + \frac{7}{{20}} = \)………………………...

\(\frac{5}{{16}} + \frac{7}{{48}} = \)………………………….                   \(\frac{{11}}{{12}} - \frac{1}{{12}} = \)…………………………

\(\frac{{13}}{{40}} + \frac{{17}}{{40}} = \frac{{13 + 17}}{{40}} = \frac{{20}}{{40}} = \frac{{20:20}}{{40:20}} = \frac{1}{2}\)                 

\(\frac{{17}}{{20}} + \frac{7}{{20}} = \frac{{17 + 7}}{{20}} = \frac{{24}}{{20}} = \frac{{24:4}}{{20:4}} = \frac{6}{5}\)

\(\frac{5}{{16}} + \frac{7}{{48}} = \frac{{5 \times 3}}{{16 \times 3}} + \frac{7}{{48}} = \frac{{15}}{{48}} + \frac{7}{{48}} = \frac{{15 + 7}}{{48}} = \frac{{22}}{{48}} = \frac{{22:2}}{{48:2}} = \frac{{11}}{{24}}\)

\(\frac{{11}}{{12}} - \frac{1}{{12}} = \frac{{11 - 1}}{{12}} = \frac{{10}}{{12}} = \frac{{10:2}}{{12:2}} = \frac{5}{6}\)