Jack Is Twice As Old As Jill. In 2 Years, Jack Will Be 4 Times As Old As Jill Was 9 Years Ago. How Old Are They Now?

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Let b be Jack's age now, g be Jill's age now.
b = 2g    (Jack is twice as old as Jill)
(b+2) = 4(g-9)    (in 2 years, Jack will be twice Jill's age 9 years ago)

((2g)+2) = 4g -36    (substitute for b, use the distributive property on the right side)
2g + 38 = 4g    (add 36 to both sides)
38 = 2g    (subtract 2g from both sides. Recognize this tells us the value of b.
19 = g    (divide both sides by 2)

Jack is 38, Jill is 19.

In two years, Jack will be 40, which is 4 times Jill's age 9 years ago, when she was 10.

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