SOLUTION: Jack is twice as old as Jill. If 4 years ago Jack’s age was thrice as Jill’s. Find their present age.

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Question 757467: Jack is twice as old as Jill. If 4 years ago Jack’s age was thrice as Jill’s. Find their present age.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = Jack's age now
Let +b+ = Jill's age now
given:
(1) +a+=+2b+
(2) ++a+-+4+=+3%2A%28+b+-+4+%29+
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By substitution,
(2) +2b+-+4+=+3b+-+12+
(2) +b+=+12+-+4+
(2) +b+=+8+
and, since
(1) +a+=+2b+
(1) +a+=+2%2A8+
(1) +a+=+16+
Jack is 16
Jill is 8
----------
check:
(2) ++a+-+4+=+3%2A%28+b+-+4+%29+
(2) ++16+-+4+=+3%2A%28+8+-+4+%29+
(2) +12+=+3%2A4+
(2) +12+=+12+
OK