Đúng ghi Đ, sai ghi S. a) 4/5 + 3/20 = (4 + 3)/20 = 7/20

Đúng ghi Đ, sai ghi S.

a) \[\frac{4}{5} + \frac{3}{{20}} = \frac{{4 + 3}}{{20}} = \frac{7}{{20}}\]    S                 

b) \[\frac{4}{9} + \frac{{17}}{{54}} = \frac{{4 + 17}}{{9 + 54}} = \frac{{21}}{{63}}\]     S

c) \[\frac{2}{7} + \frac{5}{{14}} = \frac{4}{{14}} + \frac{5}{{14}} = \frac{9}{{14}}\]   Đ                

d) \[\frac{3}{5} + \frac{2}{{15}} = \frac{{3 + 2}}{5} = \frac{5}{5} = 1\]       S

Giải thích

a) \[\frac{4}{5} + \frac{3}{{20}} = \frac{{16}}{{20}} + \frac{3}{{20}} = \frac{{19}}{{20}}\]                   

b) \[\frac{4}{9} + \frac{{17}}{{54}} = \frac{{24}}{{54}} + \frac{{17}}{{54}} = \frac{{41}}{{54}}\]                   

d) \[\frac{3}{5} + \frac{2}{{15}} = \frac{9}{{15}} + \frac{2}{{15}} = \frac{{11}}{{15}}\]