b 2$\frac{4}{7}$ ×3$\frac{5}{4}$
=$\frac{18}{7}$ $\frac{17}{4}$
=$\frac{153}{14}$ =10$\frac{13}{14}$
⇒Chọn ý D
c 4$\frac{2}{3}$ ÷2$\frac{4}{5}$
=$\frac{14}{3}$ $\frac{14}{5}$
=$\frac{14}{3}$ ×$\frac{5}{14}$
=$\frac{5}{3}$ =1$\frac{2}{3}$
⇒Chọn ý C
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