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

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Question 223970: John is twice as old as his son. In 42 years, the ratio of their age will be 4:3. what is the son's current age?
Answer by drj(1380) About Me  (Show Source):
You can put this solution on YOUR website!
John is twice as old as his son. In 42 years, the ratio of their age will be 4:3. What is the son's current age?


Step 1. Let x be the age of John's son.

Step 2. Let 2x be the age of John.

Step 3. Let x+42 be the age of John's son in 42 years.

Step 4. Let 2x+42 be the age of John in 42 years.

Step 5. Then 4%2F3=%282x%2B42%29%2F%28x%2B42%29

Multiply 3(x+42) to both sides of the equation to get rid of denominators

3%28x%2B42%29%2A4%2F3=3%2A%28x%2B42%29%2A%282x%2B42%29%2F%28x%2B42%29

%28x%2B42%29%2A4=3%2A%282x%2B42%29

4x%2B4%2A42=6x%2B3%2A42

Subtract 4x+3*42 from both sides of the equation

4x%2B4%2A42-4x-3%2A42=6x%2B3%2A42-4x-3%2A42

42=2x The age of John

Divide by 2 to both sides of the equation

42%2F2=2x%2F2

21=x

Step 6. ANSWER: The current age of John's son is 21 years old.

I hope the above steps were helpful.

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Good luck in your studies!

Respectfully,
Dr J