Tính bằng cách thuận tiện

Lời giải

a)\(\frac{{12}}{{25}} + \frac{7}{{25}} + \frac{8}{{25}} = \frac{{20}}{{25}} + \frac{7}{{25}}\)

                         \( = \frac{{27}}{{25}}\)

b) \(\frac{5}{{13}} + \frac{6}{{13}} + \frac{4}{{13}} = \frac{5}{{13}} + \frac{{10}}{{13}}\)

                         \( = \frac{{15}}{{13}}\)