Giải câu 5 trang 43 Cánh Diều Toán 6 tập 2.
a) $\frac{3}{16}$ : $\frac{[?]}{8}$ = $\frac{3}{4}$
$\frac{[?]}{8}$ = $\frac{3}{16}$ : $\frac{3}{4}$
$\frac{[?]}{8}$ = $\frac{3}{16}$ . $\frac{4}{3}$
$\frac{[?]}{8}$ = $\frac{3 . 4}{16 . 3}$
$\frac{[?]}{8}$ = $\frac{12}{48}$
$\frac{[?]}{8}$ = $\frac{2}{8}$
=> [?] = 2
b) $\frac{1}{25}$ : $\frac{- 3}{[?]}$ = $\frac{- 1}{15}$
$\frac{- 3}{[?]}$ = $\frac{1}{25}$ : $\frac{- 1}{15}$
$\frac{- 3}{[?]}$ = $\frac{1}{25}$ . $\frac{15}{- 1}$
$\frac{- 3}{[?]}$ = $\frac{1 . 15}{25 . (- 1)}$
$\frac{- 3}{[?]}$ = $\frac{15}{- 25}$
$\frac{- 3}{[?]}$ = $\frac{3}{- 5}$
=> [?] = 5
c) $\frac{[?]}{12}$ : $\frac{- 4}{9}$ = $\frac{- 3}{16}$
$\frac{[?]}{12}$ = $\frac{- 3}{16}$ . $\frac{- 4}{9}$
$\frac{[?]}{12}$ = $\frac{(- 3) . (- 4)}{16 . 9}$
$\frac{[?]}{12}$ = $\frac{12}{144}$
$\frac{[?]}{12}$ = $\frac{1}{12}$
=> [?] = 1