SOLUTION: The age of Jack and John is 49. Jack is twice as old, as John was when Jack was as old as John is now. How old are the brothers?

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Question 770096: The age of Jack and John is 49. Jack is twice as old, as John was when Jack was as old as John is now. How old are the brothers?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = Jack's age
Let +b+ = John's age
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+a+%2B+b+=+49+
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The difference in their ages always
stays the same, +a+-+b+
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Starting at the end of the problem,
" when Jack was as old as John is now "
So Jack's age was +b+
John had to have been +b+-+%28+a+-+b+%29+=+2b+-+a+
at that time
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It says that Jack is now twice that age, so
+a+=+2%2A%28+2b+-+a+%29+
+a+=+4b+-+2a+
+3a+=+4b+
+b+=+%28+3%2F4+%29%2Aa+
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By substitution:
+a+%2B+b+=+49+
+a+%2B+%283%2F4%29%2Aa+=+49+
+%287%2F4%29%2Aa+=+49+
+a+=+%284%2F7%29%2A49+
+a+=+28+
and
+a+%2B+b+=+49+
+b+=+21+
Jack is 28 and John is 21
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check:
" when Jack was as old as John is now "
Jack was 21
John had to have been 7 years younger,
or 14
Jack's age now is twice that age, or 28
OK