Ratio and Proportion Practice Test 4

The students in the three classes = 4 : 6 : 9
Students increased in each class = 12
Ratio change = 7 : 9 : 12
According to the statement,
$4\mathit{x}+12:6\mathit{x}+12:9\mathit{x}+12$ or $\mathit{a}:\mathit{b}:\mathit{c}$
We can write it as a : b : : b : c.
$\left(4\mathit{x}+12\right):\left(6\mathit{x}+12\right)$ $::\left(6\mathit{x}+12\right):\left(9\mathit{x}+12\right)$
Ratio change = 7 : 9 : : 9 : 12
$\frac{\left(4\mathit{x}+12\right)\left(6\mathit{x}+12\right)}{\left(6\mathit{x}+12\right)\left(9\mathit{x}+12\right)}=\frac{7\times 9}{9\times 12}$
$\frac{\left(4\mathit{x}+12\right)}{\left(9\mathit{x}+12\right)}=\frac{7}{12}$
$\mathit{x}=4$
Total number of students in three classes before the increase is $=4\mathit{x}+6\mathit{x}+9\mathit{x}$
$=4\times 4+6\times 4+9\times 4=76$