【答案】:
$? =\frac {9}{17}×15+\frac 9{17}×19?$
$? =\frac 9{17}×(15+19)?$
$? =\frac 9{17}×34?$
? =18?
$? =\frac 4{13}×7+\frac 4{13}×32?$
$? =\frac 4{13}×(7+32)?$
$? =\frac 4{13}×39?$
? =12?
【解析】:
$\frac{15}{17} × 9 + \frac{9}{17} × 19$
$=\frac{9}{17} × 15 + \frac{9}{17} × 19$
$=\frac{9}{17} × (15 + 19)$
$=\frac{9}{17} × 34$
$=18$
$\frac{1}{13} × 28 + \frac{4}{13} × 32$
$=\frac{4}{13} × 7 + \frac{4}{13} × 32$
$=\frac{4}{13} × (7 + 32)$
$=\frac{4}{13} × 39$
$=12$