I read a mystery in a book but I can't solve it with Mathematics. The mystery is:
"I have tripled my nephew's age, and 5 years ago I have 5 times from his twin brother age. What is my age now?"
In mathematics the problem is like this:
$x=$my age , $y=$my nephew's age
$x=3y$
$x-5=5y$
but the answer from that equation is not true.
the correct answers are : $x=30$ and $y=10$. How did they solve this problem?
(sorry for my bad english)
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1The second equations should be $x-5=5(y-5)$ – Artem Feb 02 '14 at 03:56
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Your age is $30$. – Mhenni Benghorbal Feb 02 '14 at 04:00
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2@Artem: Yes, that's it. The nephew was also 5 years younger then. – MPW Feb 02 '14 at 04:00
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1What does "I have 5 times from his twin brother age" mean? – copper.hat Feb 02 '14 at 04:45
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Interesting that only copper.hat asked that needed question more than half hour after the OP was posted: what did people understand?! – DonAntonio Feb 02 '14 at 05:16
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Perhaps the riddle should be: "Right now I'm three times as old as my nephew is, and 5 years ago I was 5 times as old as his (the nephew's, apparently) twin brother was. What's my age now?" – DonAntonio Feb 02 '14 at 05:18
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It could be I am 5 times my twin's brother age... which could be older or younger. – usukidoll Feb 02 '14 at 06:15
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@DonAntonio:Yes, it's true – emma Feb 03 '14 at 02:09
1 Answers
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Hints: using your notation, and assuming the riddle is what I wrote in the comment above, the equations are
$$\begin{align*}x&=3y\\(x-5)&=5(y-5)\end{align*}$$
Substitute the first eq. into the second one and get $\;y=10\;$ ...
DonAntonio
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