a) 7,2:0,8x=4,5 b) 13,5 : x -4,5=15

Đáp án+Giải thích các bước giải:

$a.$

$7,2:0,8x=4,5$

$⇔0,8x=7,2:4,5$

$⇔\dfrac{4}{5}x=\dfrac{36}{5}.\dfrac{2}{9}$

$⇔\dfrac{4}{5}x=\dfrac{8}{5}$

$⇔x=\dfrac{8}{5}.\dfrac{5}{4}$

$⇔x=2$

Vậy $x=2$

$b.$

$13,5:x-4,5=15$

$⇔13,5:x=15+4,5$

$⇔13,5:x=19,5$

$⇔x=13,5:19,5$

$⇔x=\dfrac{27}{2}.\dfrac{2}{39}$

$⇔x=\dfrac{9}{13}$

Vậy $x=\dfrac{9}{13}$

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#andy

$\begin{array}{l} a){\rm{ }}7,2:0,8x = 4,5\\ 0,8x = 7,2:4,5\\ 0,8x = 1,6\\ x = 1,6:0,8\\ x = 2\\ b){\rm{ }}13,5:x - 4,5 = 15\\ 13,5:x = 15 + 4,5\\ 13,5:x = 19,5\\ x = 13,5:19,5\\ x = \dfrac{9}{{12}} \end{array}$