Đáp án:
a) `33/40`
b) `110/441`
Giải thích các bước giải:
a) Cách 1:
$\bigg(\dfrac{5}{4}+\dfrac{2}{5}\bigg) \times \dfrac{7}{14}\\=\bigg(\dfrac{25}{20}+\dfrac{8}{20}\bigg)\times \dfrac{1}{2}\\=\dfrac{33}{20} \times \dfrac{1}{2}=\dfrac{33}{40}$
Cách 2:
$\bigg(\dfrac{5}{4}+\dfrac{2}{5}\bigg)\times \dfrac{7}{14}\\=\dfrac{5}{4}\times \dfrac{7}{14}+\dfrac{2}{5}\times \dfrac{7}{14}\\=\dfrac{5}{8}+\dfrac{1}{5}\\=\dfrac{25}{40}+\dfrac{8}{40}=\dfrac{33}{40}$
b) Cách 1:
$\bigg(\dfrac{4}{9}+\dfrac{3}{7}\bigg)\times \dfrac{2}{7}\\ =\bigg(\dfrac{28}{63}+\dfrac{27}{63}\bigg)\times \dfrac{2}{7}\\=\dfrac{55}{63}\times \dfrac{2}{7}=\dfrac{110}{441}$
Cách 2:
$\bigg(\dfrac{4}{9}+\dfrac{3}{7}\bigg)\times \dfrac{2}{7}\\=\dfrac{4}{9} \times \dfrac{2}{7}+\dfrac{3}{7} \times \dfrac{2}{7}\\=\dfrac{8}{63}+\dfrac{6}{49}\\=\dfrac{56}{441}+\dfrac{54}{441}=\dfrac{110}{441}$
