Tính giá trị biểu thức:  a) 2/5 + 2/3 x 1/5 =

Hướng dẫn: 

a) \(\frac{2}{5} + \frac{2}{3} \times \frac{1}{5} = \frac{2}{5} + \frac{2}{{15}} = \frac{6}{{15}} + \frac{2}{{15}} = \frac{8}{{15}}\)

b) \(\frac{1}{3} \times \frac{4}{7} \times 5 = \frac{1}{3} \times \frac{4}{7} \times \frac{5}{1} = \frac{{20}}{{21}}\)

c) \(\frac{{16}}{{15}}:\frac{1}{2} + \frac{{18}}{{25}}:3 = \frac{{16}}{{15}} \times \frac{2}{1} + \frac{{18}}{{25}} \times \frac{1}{3} = \frac{{32}}{{15}} + \frac{6}{{25}} = \frac{{178}}{{75}}\)