Đáp án:
CHÚC BẠN HỌC TỐT!
$a)$ $\frac{14}{17}$+ $\frac{3}{14}$
= $\frac{14.14}{238}$+ $\frac{3.17}{238}$
= $\frac{196}{238}$+ $\frac{51}{238}$
= $\frac{247}{238}$
$b)$ $\frac{15}{21}$ + $\frac{3}{42}$
= $\frac{30}{42}$ + $\frac{3}{42}$
= $\frac{33}{42}$= $\frac{11}{14}$
$c)$ $\frac{2}{7}$ + $\frac{3}{9}$
= $\frac{2.9}{63}$ + $\frac{3.7}{63}$
= $\frac{18}{63}$ + $\frac{21}{63}$
=$\frac{39}{63}$= $\frac{13}{21}$
