Giải bài 5 trang 43 SGK Toán 6 Cánh diều

Đề bài

Tìm số thích hợp cho [?]:

a) \(\frac{3}{{16}}:\frac{{\left[ ? \right]}}{8} = \frac{3}{4}\);

b) \(\frac{1}{{25}}:\frac{{ - 3}}{{\left[ ? \right]}} = \frac{{ - 1}}{{15}}\);

c) \(\frac{{\left[ ? \right]}}{{12}}:\frac{{ - 4}}{9} = \frac{{ - 3}}{{16}}\).

Lời giải chi tiết

a)

 \(\begin{array}{l}\frac{3}{{16}}:\frac{{\left[ ? \right]}}{8} = \frac{3}{4}\\\frac{{\left[ ? \right]}}{8} = \frac{3}{{16}}:\frac{3}{4}\\\frac{{\left[ ? \right]}}{8} = \frac{3}{{16}}.\frac{4}{3}\\\frac{{\left[ ? \right]}}{8} = \frac{{12}}{{48}}\\\frac{{\left[ ? \right]}}{8} = \frac{2}{8}\\ \Rightarrow \left[ ? \right] = 2\end{array}\)

b)

\(\begin{array}{l}\frac{1}{{25}}:\frac{{ - 3}}{{\left[ ? \right]}} = \frac{{ - 1}}{{15}}\\\frac{{ - 3}}{{\left[ ? \right]}} = \frac{1}{{25}}:\frac{{ - 1}}{{15}}\\\frac{{ - 3}}{{\left[ ? \right]}} = \frac{1}{{25}}.\frac{{ - 15}}{1}\\\frac{{ - 3}}{{\left[ ? \right]}} = \frac{{ - 15}}{{25}}\\\frac{{ - 3}}{{\left[ ? \right]}} = \frac{{ - 3}}{5}\\ \Rightarrow \left[ ? \right] = 5\end{array}\)

c)

\(\begin{array}{l}\frac{{\left[ ? \right]}}{{12}}:\frac{{ - 4}}{9} = \frac{{ - 3}}{{16}}\\\frac{{\left[ ? \right]}}{{12}} = \frac{{ - 3}}{{16}}.\frac{{ - 4}}{9}\\\frac{{\left[ ? \right]}}{{12}} = \frac{{12}}{{144}}\\\frac{{\left[ ? \right]}}{{12}} = \frac{1}{{12}}\\ \Rightarrow \left[ ? \right] = 1\end{array}\)