Giải bài 38 trang 40 SBT Toán 6 Cánh diều tập 2 - CD

Hướng dẫn giải

Quy tắc nhân phân số:

\(\frac{a}{b}.\frac{c}{d} = \frac{{a.c}}{{b.d}}\;\;(b \ne 0,d \ne 0);\;\;\;m.\frac{a}{b} = \frac{a}{b}.m = \frac{{a.m}}{b}\)

Lời giải chi tiết

a) \(\frac{{ - 4}}{7}.\frac{7}{{ - 16}} = \frac{{( - 4).7}}{{7.( - 16)}} = \frac{1}{4}\)

b) \(\frac{5}{{ - 11}}.22 = \frac{{5.22}}{{ - 11}} =  - 10\)

c) \(\frac{{ - 5}}{{16}}.( - 32) = \frac{{ - 5.( - 32)}}{{16}} = 10\)

d) \(35.\frac{{ - 4}}{{21}} = \frac{{35.\left( { - 4} \right)}}{{21}} = \frac{{5.7.\left( { - 4} \right)}}{{3.7}} = \frac{{ - 20}}{3}\)

e) \(\frac{{25}}{{10}}.1\frac{1}{3} = \frac{{25}}{{10}}.\frac{4}{3} = \frac{{25.4}}{{10.3}} = \frac{{4.5.5}}{{2.3.5}} = \frac{{10}}{3}\)

g) \(\frac{{ - 37}}{{401}}.( - 1) = \frac{{\left( { - 37} \right).( - 1)}}{{401}} = \frac{{37}}{{401}}.\)

h) \(\left( {1 - \frac{1}{5}} \right)\left( {\frac{{ - 3}}{{10}} + \frac{1}{5}} \right) = \left( {\frac{5}{5} - \frac{1}{5}} \right)\left( {\frac{{ - 3}}{{10}} + \frac{2}{{10}}} \right) = \frac{4}{5}.\frac{{( - 1)}}{{10}} = \frac{{ - 2}}{{25}}\)

i) \(\frac{{ - 3}}{5}.\frac{{ - 3}}{5}.\frac{1}{3} = \frac{{\left( { - 3} \right).\left( { - 3} \right).1}}{{5.5.3}} = \frac{3}{{25}}\)

-- Mod Toán 6 HỌC247