SOLUTION: Roy is twice as old as Joan, and in 3 years the sum of their ages will be 21 years. Find their present ages.

Question 972797: Roy is twice as old as Joan, and in 3 years the sum of their ages will be 21 years. Find their present ages.
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
let Roy's age be x and Joan's age be y, then
x = 2y
x+3 + y+3 = 21
substitute 2y for x
2y+3 + y+3 = 21
3y + 6 = 21
subtract 6 from both sides of =
3y = 15
divide both sides of = by 3
y = 5 and x = 10
Roy is 10 and Joan is 5
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check answer
10+3 + 5+3 = 21
13 + 8 = 21
21 = 21
our answer checks
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