SOLUTION: The ratio of the number of stamps John had to the number of stamps Peter had was 4:1. after John bought 13 more to add to his collection and Peter was given 7 more by his brother,

Question 850408: The ratio of the number of stamps John had to the number of stamps Peter had was 4:1. after John bought 13 more to add to his collection and Peter was given 7 more by his brother, the ratio became 3:1. How many stamps did John and Peter have at first?
I try to solve the problem sum by using two changing quantities ratio method but cannot get the answer. Please let me know the reason and show me how to solve the sum. Thank you.
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
let the number of stamps Peter has be x and then John has 4x
now John got 13 more stamps and Peter got 7, therefore
(4x+13) / (x+7) = 3/1
now cross multiply the fractions
4x+13 = 3*(x+7)
4x+13 = 3x+21
x = 8
at first Peter had 8 stamps and John had 32 stamps

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