Flashcard question

[andreasdeptolla]

I am not sure whether I should post this question here or in the math section. I reviewed the flashcards for WT today and one of the questions was as follows:

Sean is 15 year older than Eric. In 6 years Sean will be twice as old as Eric. How old is Eric.? (Answers: 9, 14, 24)

The answer suggest to pick a number and try. When I was working on the problem I set up the following equations:

S = E +15
S+6=2E

However, I do not get the right result? Can you please outline how to correctly set up the equations?

Thanks
Andreas

[eileen1017]

I am not sure whether I should post this question here or in the math section. I reviewed the flashcards for WT today and one of the questions was as follows:

Sean is 15 year older than Eric. In 6 years Sean will be twice as old as Eric. How old is Eric.? (Answers: 9, 14, 24)

The answer suggest to pick a number and try. When I was working on the problem I set up the following equations:

S = E +15
S+6=2E

However, I do not get the right result? Can you please outline how to correctly set up the equations?

Thanks
Andreas

Well, your second equations is wrong. In six years, as Sean grows older so does Eric. So your second equation should be S+6=2(E+6). The answer should be 9.

[StaceyKoprince]

Hi, guys

(1) a problem like this should be posted in the Math Strategy Guide folder (I know it isn't strictly from the math strat guide, but it is from our flash cards, so it qualifies). We'll leave it here for now, because Eileen has responded with a correct solution, but if you have other flashcard questions in the future, go ahead and post them in the Math Strat Guide folder.

(2) Eileen is right - there's an error in that second equation. It's tricky to write equations for time periods that aren't "today." I've found that the easiest way to do it is to first write all variables with the appropriate time added or subtracted (in this case, you'd want to add 6 years to all variables), and only then add everything else, like the equals sign and the 2* (in this case). Does that make sense?