question_answer 13)

                Fifteen years from now Ravi's age will be four times his present age. What is Ravi's present age?

Answer:

                Let the present age of Ravi be \[x\] years. Then, age of Ravi fifteen years from now \[=(x+15)\]years \[\because \]     Fifteen years from now Ravi?s age will be four times his present age. \[\therefore \]  \[x+15=4x\] \[\Rightarrow \]               \[15=4x-x\]                         | Transposing \[x\] to RHS \[\Rightarrow \]               \[15=3x\] \[\Rightarrow \]               \[3x=15\] \[\Rightarrow \]               \[x=\frac{15}{3}=5\]                       | Dividing both sides by 3 Hence, the present age of Ravi is 5 years. Check: \[5+15=20\]         | as desired \[20=4\times 5\].