Question 999755
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X = sister's age; Y = Susan's age = X+5yrs
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X+Y=51 yrs
X+(X+5yrs)=51 yrs
2X=46yrs
X=23 yrs
Sister is 23 years old.
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Y=X+5yrs=23yrs+5yrs=28yrs
Susan is 28 years old.
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You cannot write a single equation to solve for two variables.