SOLUTION: Four years ago, Lisa was twice as old as John. Four years from now, John will be three quarters of Lisa's age. How old is Lisa Now?

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Question 388031: Four years ago, Lisa was twice as old as John. Four years from now, John will be three quarters of Lisa's age. How old is Lisa Now?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
"Four years ago, Lisa was twice as old as John"
L-4=2%28J-4%29
L-4=2J-8
1.L=2J-4
.
.
.
"Four years from now, John will be three quarters of Lisa's age."
J%2B4=%283%2F4%29%28L%2B4%29
4%28J%2B4%29=3%28L%2B4%29
4J%2B16=3L%2B12
2.4J=3L-4
Substitute from eq. 1 into eq. 2,
4J=3%282J-4%29-4
4J=6J-12-4
-2J=-16
highlight%28J=8%29
Then from eq. 1,
L=16-4
highlight%28L=12%29
.
.
.
Right now, Lisa is 12 and John is 8.