Question

Robert's father is 4 times as old as Robert.After 5 years ,father will be three times as old as Robert. What is their present ages of Robert and his father respectively .​

Answer 1

Their present ages are:

Robert is 10 years old and his father is 40 years old.

Explanation:

Let be "r" Robert's present age and "f" his father's present age.

Based on the information given in the exercise, you can set up the following system of equations:

`\left \{ {{f=4r} \atop {f+5=3(r+5)}} \right.`

Use the Substitution Method and substitute the first equation into the second one and then solve for "r":

`4r+5=3(r+5)}\\\\4r+5=3r+15\\\\4r-3r=15-5\\\\r=10`

Substitute the value of "r" into the first equation and evaluate:

`f=4(10)\\\\f=40`