SOLUTION: Thirteen years from now, David will be twice as old as Joanna. the current sum of the ages of David and Joanna is 19. How old is Joanna now?

Question 1198386: Thirteen years from now, David will be twice as old as Joanna. the current sum of the ages of David and Joanna is 19. How old is Joanna now?
Found 2 solutions by josgarithmetic, greenestamps:
Answer by josgarithmetic(39620) (Show Source): You can put this solution on YOUR website!

Question asks for j.

Substituting,
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Answer by greenestamps(13200) (Show Source): You can put this solution on YOUR website!

Always allow yourself to consider different ways of setting up a problem for solving. In elementary problems like this, there are always many different possibilities.

The other tutor has shown one way to set up the problem, using a system of two equations with the two ages as the variables.

Here is my preference for setting up the problem, using one variable, and starting from the information that David will be twice as old as Diana 13 years from now.

let x = Diana's age 13 years from now
then 2x = David's age 13 years from now

Diana's age now is then x-13, and David's age now is 2x-13.

The sum of their ages now is 19:

ANSWER: Diana's age now is x-13 = 15-13 = 2

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