【答案】:
$? =\frac 12×\frac 65?$
$? =\frac 35?$
$? =\frac 2{13}×\frac {11}4×\frac 65?$
$? =\frac {11}{26}×\frac 65?$
$? =\frac {33}{65}?$
$? =\frac 9{10}×\frac 83×5?$
$? =\frac 9{10}×5×\frac 83?$
$? =\frac 92×\frac 83?$
? =12?
【解析】:
$\frac{5}{8}×\frac{4}{5}÷\frac{5}{6}$
$=\frac{5}{8}×\frac{4}{5}×\frac{6}{5}$
$=\frac{1}{2}×\frac{6}{5}$
$=\frac{3}{5}$
$\frac{2}{13}÷\frac{4}{11}×\frac{6}{5}$
$=\frac{2}{13}×\frac{11}{4}×\frac{6}{5}$
$=\frac{11}{26}×\frac{6}{5}$
$=\frac{33}{65}$
$\frac{9}{10}÷\frac{3}{8}÷\frac{1}{5}$
$=\frac{9}{10}×\frac{8}{3}×5$
$=\frac{12}{5}×5$
$=12$