John is twice as old as his son. In 42 years, the ratio of their ages will be 4:3. What is the son's current age?

Jhon is 42 years old, and his son is 21 years old.

Step-by-step explanation:

Let's define:

J = John's age

S = Age of the son.

We know that:

"John is twice as old as his son"

J = 2*S

"In 42 years, the ratio of their ages will be 4:3. What is the son's current age?"

In 42, their ages will be:

J + 42 and S + 42.

And the ratio 4:3 means that:

(J + 42) = (4/3)*(S + 42)

Then we have the system of equations:

J = 2*S

(J + 42) = (4/3)*(S + 42)

To solve it we can first replace the first equation into the second one, to get:

(2*S + 42) = (4/3)*(S + 42)

2*S  - (4/3)*S = (4/3)*42 - 42

S*(6/3 - 4/3) = (1/3)*42

S*(2/3) = (1/3)*42

S = (3/2)*(1/3)*42 = 21.

And we can find Jonh's age if we use the first equation:

J = 2*S = 2*21 = 42

Jhon is 42 years old, and his son is 21 years old.

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