SOLUTION: Marcus has two sisters. The sum of the girls' ages is 13. The product of their ages is 36. How old is each sister?

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Question 390719: Marcus has two sisters. The sum of the girls' ages is 13. The product of their ages is 36. How old is each sister?
Answer by checkley79(3341) About Me  (Show Source):
You can put this solution on YOUR website!
X+Y=13
X=13-Y
XY=36
(13-Y)Y=36
13Y-Y^2=36
-Y^2+13Y-36=0
Y^2-13Y+36=0
(Y-9)(Y-4)=0
Y-9=0
Y=9 YEARS OLD ANS. FOR ONE SISTER
X+9=13
X=13-9
X=4 YEARS OLD ANS. FOR THE OTHER SISTER
Y-4=0
Y=4 ANS. DITTO.
X+4=13
X=13-4
X=9 DITTO.
PROOF:
4+9=13
13=13
4*9=36
36=36