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Mansion has a son (Mark) and a daughter (Mindy). Mark is older than Mindy.

Five years ago, Sum of Mark and Mindy’s ages was twenty two. Five years from now, Mark will be exactly twice as old as Mindy.

How old is Mark now? Give your reasoning details.

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Let a be Mark and b be Mindy. Then

$a-5+b-5 = 22$, so $a+b = 32$. Further, $a+5 = 2(b+5) = 2b + 10$. But $a = 32 - b$, so $32 - b + 5 = 37 - b = 2b + 10$. So $3b = 27$, so $b = 9$. Then $a = 32 - 9 = 23$.

So

Mark is 23.

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ma is the age of Mark

my ist the age of Mindy

1. (ma-5)+(my-5) = 22
ma-5 + my-5 = 22 |+10
ma+my = 32
2. ma+5 = 2*(my+5)
ma+5 = 2*my+10 |-5
ma = 2*my+5
(2*my+5)+my = 32
3*my + 5 = 32 |-5
3*my = 27 |/3
my = 9
9 + ma = 32 |-9
ma = 23

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  • $\begingroup$ Welcome to PSE ! Please use spoilers $$ >! $$ before each line and add 2 spaces at the end of each line. Also try to use MathJax. $\endgroup$ – Ak. Jun 19 '19 at 14:32
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    $\begingroup$ Good answer, but I think I beat you to it! $\endgroup$ – El-Guest Jun 19 '19 at 15:05
  • $\begingroup$ Yes you were faster :) , are similar answers in PSE undesirable ? $\endgroup$ – user60999 Jun 19 '19 at 15:10
  • $\begingroup$ @TanteMartina There's some leeway allowed, in cases where one person answers while another's still typing (which happens a lot, let me tell you). If you'd posted your answer seven hours after El-Guest, then it would be a problem, but seven minutes seems acceptable to me. $\endgroup$ – F1Krazy Jun 19 '19 at 15:31
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    $\begingroup$ Tbh, what's more undesirable here is that you're not supposed to answer off-topic questions, because it encouraged people to ask more of them. Again, you have some leeway in that regard, since you only just got here and probably didn't know that, but El-Guest has 23k rep and you'd think he'd know better than that. $\endgroup$ – F1Krazy Jun 19 '19 at 15:33

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