Question

Present age of the father is 4 times his son. If the sum of their ages after 20
D5
years is 100 years, what will be their present ages (in years):​

Answer 1

Answer:Son = S

Father = F

We need to make a system of equations with the information we are given. If the father is 4 times as old as his son, the equation can be displayed as:

4S = F

Now we know that in 20 years the father will be twice as old as his son. This information can be displayed in the following equation:

2S + 20 = F

Now we solve the system of equations. Multiply the second equation by -2.

-2(2S + 20 = F) This is equivalent to: -4S - 40 = -2F.

Now we add the new second equation, and the first equation together.

-4S - 40 = -2F

+

4S = F

This gives you -40 = -F

Now multiply the whole equation by -1 and solve to get that F = 40.

That means that the father is 40 years old. We can now plug this number into the first equation:

4S = 40

and divide the whole equation by 4 to get that S = 10. So the son is 10 years old and the father is 40 years old.

Step-by-step explanation: