## Bài 1 b)1/7-8/7:8-3:3/4×4 c)1,4×15/49-(4/5+2/3):11/5 Bài 2: Tìm x biết 2/3

Question

Bài 1
b)1/7-8/7:8-3:3/4×4
c)1,4×15/49-(4/5+2/3):11/5
Bài 2: Tìm x biết
2/3

in progress 0
10 months 2021-04-23T22:51:22+00:00 1 Answers 6 views 0

$\begin{array}{l} a)\dfrac{1}{7} – \dfrac{8}{7}:8 – 3:\dfrac{3}{4}.4\\ = \dfrac{1}{7} – \dfrac{8}{7}.\dfrac{1}{8} – 3.\dfrac{4}{3}.4\\ = \dfrac{1}{7} – \dfrac{1}{7} – 16\\ = – 16\\ c)1,4.\dfrac{{15}}{{49}} – \left( {\dfrac{4}{5} + \dfrac{2}{3}} \right):\dfrac{{11}}{5}\\ = \dfrac{7}{5}.\dfrac{{15}}{{49}} – \dfrac{{12 + 10}}{{15}}.\dfrac{5}{{11}}\\ = \dfrac{3}{7} – \dfrac{{22}}{{15}}.\dfrac{5}{{11}}\\ = \dfrac{3}{7} – \dfrac{2}{3}\\ = \dfrac{{9 – 14}}{{21}}\\ = \dfrac{{ – 5}}{{21}}\\ B2)\\ \dfrac{2}{3} < \dfrac{x}{{18}} < \dfrac{8}{9}\left( {x \in Z} \right)\\ \Leftrightarrow \dfrac{{2.6}}{{18}} < \dfrac{x}{{18}} < \dfrac{{8.2}}{{18}}\\ \Leftrightarrow \dfrac{{12}}{{18}} < \dfrac{x}{{18}} < \dfrac{{16}}{{18}}\\ \Leftrightarrow 12 < x < 16\\ \Leftrightarrow x \in \left\{ {13;14;15} \right\}\\ B3)\\ a:b = 1:\dfrac{3}{4}\\ \Leftrightarrow a:b = \dfrac{4}{3}\\ \Leftrightarrow \dfrac{a}{b} = \dfrac{4}{3}\\ \Leftrightarrow a = \dfrac{4}{3}.b\\ a + b = 22\\ \Leftrightarrow \dfrac{4}{3}.b + b = 22\\ \Leftrightarrow b.\left( {\dfrac{4}{3} + 1} \right) = 22\\ \Leftrightarrow b.\dfrac{7}{3} = 22\\ \Leftrightarrow b = 22.\dfrac{3}{7} = \dfrac{{66}}{7}\\ \Leftrightarrow a = \dfrac{4}{3}.b = \dfrac{4}{3}.\dfrac{{66}}{7} = \dfrac{{88}}{7}\\ Vậy\,a = \dfrac{{88}}{7};b = \dfrac{{66}}{7} \end{array}$