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Review: Ernesto and His Wife's Ages
Explanation
If we call Ernesto's age E and his wife's age W,
then we are told that 
and 
.
We can substitute to solve. When you solve by substitution, you first isolate
the variable you don't want at the
end. So we isolate W: 
and then substitute:
This one is easy to check. The wife must be 42. If he were
15 years older, he'd be 63, which is 21 and hence 50% older than his wife.
The correct answer is (A).
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