Question

If 25 percent of a certain number is 36, what would 40 percent of the same number would be:
(a)13.67
(b)22.5
(c)42.6
(d)52.8
(e)57.6

Answer 1

Hint: Let us assume a certain number be “x” then we have given that 25 percent of a certain number is 36. Writing 25 percent of x and equating it to 36 we get $\dfrac{25}{100}x=36$. From this equation, find the value of “x” and put this value in the 40 percent of x.

Complete step-by-step answer:
Let us assume that a certain number is x.
It is given that 25 percent of x is equal to 36 so writing this statement in the form of equation we get,
$\dfrac{25}{100}x=36$
In the above equation, the fraction $\dfrac{25}{100}$ is reduced to $\dfrac{1}{4}$ so the above equation will look like:
$\begin{align}
  & \dfrac{1}{4}x=36 \\
 & \Rightarrow x=36\times 4 \\
 & \Rightarrow x=144 \\
\end{align}$
From the above, we have got a certain number that is equal to 144.
Now, we have to find the value of 40 percent of a certain number (i.e. 144) which is given by the following formula:
$\dfrac{40}{100}\left( 144 \right)$
10 will be cancelled out from the numerator and denominator and we will be left by:
$\dfrac{4}{10}\left( 144 \right)$
Multiplying 4 and 144 in the numerator will give:
$\dfrac{576}{10}$
In the above expression, dividing 576 by 10 we get,
57.6
From the above solution, 40 percent of a certain number is equal to 57.6.
Hence, the correct option is (e).

Note: In the above, we have written 25 percent as $\dfrac{25}{100}$ so percent of any number is calculated by dividing that number by 100.
In percent we have to divide by 100 which we can remember as percent word contains per and cent. “Cent” means 100 so percent of any number means number out of 100. We can also write 25 percent as 0.25 and then compute the value of x. Similarly we can take 40 percent as 0.4 and then find 40 percent of x.