SOLUTION: Mary’s father is four times as old as Mary. Five years ago, he was seven times as old. How old is each now?

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Question 1051724: Mary’s father is four times as old as Mary. Five years ago, he was seven times as old. How old is each now?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = Mary's age now
Let +b+ = her father's age now
---------------------------------
(1) +b+=+4a+
(2) +b+-+5+=+7%2A%28+a+-+5+%29+
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Substitute (1) into (2)
(2) +4a+-+5+=+7%2A%28+a+-+5+%29+
(2) +4a+-+5+=+7a+-+35+
(2) +3a+=+35+-+5+
(2) +3a+=+30+
(2) +a+=+10+
and
(1) +b+=+4a+
(1) +b+=+4%2A10+
(1) +b+=+40+
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Mary is 10
Her father is 40
----------------
check:
(2) +b+-+5+=+7%2A%28+a+-+5+%29+
(2) +40+-+5+=+7%2A%28+10+-+5+%29+
(2) +35+=+7%2A5+
(2) +35+=+35+
OK