SOLUTION: Jacky is tWo-third as old as her sister.Twenty years from now, she will be seven-eighths as old as her sister.How old is jacky?

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Question 972574: Jacky is tWo-third as old as her sister.Twenty years from now, she will be seven-eighths as old as her sister.How old is jacky?
Answer by macston(5194) About Me  (Show Source):
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S=sister's age; J=Jacky's age=(2/3)S
J+20=(7/8)(S+20) Substitute for J
(2/3)S+20=(7/8)S+(140/8)
20-(140/8)=(7/8)S-(2/3)S
(160/8)-(140/8)=(21/24)S-(16/24)S
(20/8)=(5/24)S
60/24=5S/24
60=5S
12=S Sister's age is 12.
J=(2/3)S=(2/3)12=8
ANSWER: Jacky's age is 8.
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CHECK:
J+20=(7/8)(S+20)
8+20=(7/8)(12+20)
28=(7/8)(32)
28=28