Question

Fifteen years from now Ravi’s age will be four times his present age. What is Ravi’s present age?
A. 5
B. 8
C. 7
D. 3

Answer 1

Hint: We start solving the problem by assigning variables to represent Ravi’s present age and his age after 15 years. We then add 15 to variables that represent Ravi’s age in order to get Ravi's age after 15 years. In order to get another in both variables, we multiply Ravi's present age with 4. We equate both equations and make subsequent calculations in order to get the present age of Ravi.

Complete step by step answer:
We have to find Ravi’s age.
Let us assume Ravi’s present age is ‘x’ years. After fifteen years from now, his age will be fifteen years more than his present age.
Let us assume, his age after 15 years will be ‘y’ years.
So, his age after 15 years will be $x+15$.
$i.e.y=x+15.......\left(1\right)$
But, according to the question, after 15 years Ravi’s age will be four times his present age.
$i.e.y=4x............\left(2\right)$
From equation (1) and (2);
$y=4x=x+15$
Solving for ‘x’;
$\Rightarrow 4x=x+15$
Taking all the terms of ‘x’ to LHS of the equation, we will get;
$\begin{array}{rl}& \Rightarrow 4x-x=15\\ & \Rightarrow 3x=15\end{array}$
Dividing both sides by 3, we will get;
$$\begin{array}{rl}& \Rightarrow x={\displaystyle \frac{15}{3}}\\ & \Rightarrow x=5\end{array}$$
Hence, Ravi’s present age is 5 years and so the answer will be option (A).

Note:
Whenever we get this type of problem, we should start by assigning variables to get a better picture. We can also find the future age of Ravi by adding 15 years or multiplying the present age with four times. We can also expect problems to find the future age of Ravi and also the age of family members which can be done using the relations given in the problem.