1. Thực hiện phép tính (tính nhanh nếu có thể): a) 9/4:- 3/10;2. Tìm x: a)2/3:x = 2,4 - 4/5;
1.
a) \[\frac{9}{4}:\frac{{ - 3}}{{10}}\] \[ = \frac{9}{4}.\frac{{10}}{{ - 3}}\] \[ = \frac{{9.10}}{{4.\left( { - 3} \right)}}\]\( = \frac{{15}}{{ - 2}}\) \( = \frac{{ - 15}}{2}\);
b) \[\frac{{ - 5}}{3}.\frac{{11}}{{25}} + \frac{{ - 5}}{3}.\frac{{14}}{{25}}\]\[ = \frac{{ - 5}}{3}\left( {\frac{{11}}{{25}} + \frac{{14}}{{25}}} \right)\]\[ = \frac{{ - 5}}{3}.\frac{{25}}{{25}} = \frac{{ - 5}}{3}\].
2.
a) \[\frac{2}{3}:x = 2,4 - \frac{4}{5}\] \[\frac{2}{3}:x = \frac{{12}}{5} - \frac{4}{5}\] \[\frac{2}{3}:x = \frac{8}{5}\] \[x = \frac{2}{3}:\frac{8}{5}\] \[x = \frac{5}{{12}}\]. Vậy \[x = \frac{5}{{12}}\]. | b) \[\frac{5}{4}.\left( {x - \frac{3}{5}} \right) = \frac{{ - 1}}{8}\] \[x - \frac{3}{5} = \frac{{ - 1}}{8}:\frac{5}{4}\] \[x - \frac{3}{5} = \frac{{ - 1}}{{10}}\] \[x = \frac{{ - 1}}{{10}} + \frac{3}{5}\] \[x = \frac{1}{2}\]. Vậy \[x = \frac{1}{2}\]. |