Question

$72\%\text{of}25$ students are good in mathematics. How many students are not good in mathematics?

Answer 1

Percentage of students not good in mathematics $=100\%-72\%=28\%$
Number of students not good in mathematics $=25\times \frac{28}{100}=7$

(OR)

Total number of students $=25$

Number of students good in Mathematics $=72\%$ of $25$

$=\frac{72}{100}\times 25$

$=\frac{72}{4}$

$=18$

Now, Number of students are not good in Mathematics $=25-18=7$