Đáp án:
$a)\dfrac{2}{15}$
$b)\dfrac{8}{13}$
Giải thích các bước giải:
$a)\dfrac{3}{8}×\dfrac{4}{15}×\dfrac{12}{9}\\=\dfrac{3}{2×4}×\dfrac{4}{3×5}×\dfrac{3×4}{3×3}\\=\dfrac{1}{10}×\dfrac{4}{3}\\=\dfrac{4}{30}\\=\dfrac{2}{15}$
$b)\dfrac{3}{10}×\dfrac{8}{13}+\dfrac{8}{13}×\dfrac{7}{10}\\=\dfrac{8}{13}×\Big(\dfrac{3}{10}+\dfrac{7}{10}\Big)\\=\dfrac{8}{13}$