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$2 p+ m= 135$ whereas $p + 2m = 120$ And $p+ m+ a = 100$ Find $a$.

Basic algebra but can't get sensible answer (:

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Hint: look at your first two equalities. What do you get if you add them? –  Niccolò Sep 15 '12 at 16:52
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1 Answer

After adding equality $1$ and equality $2$, we get the following:$$3m + 3p = 255$$We may divide both sides by $3$ to get,$$m + p = 85 $$Since we already have $m + p = 85 $, we see that $m + p + a$ can be written as $85 + a$(substituting $m + p$ with $85$).

We are left with the equation:$$ 85 + a = 100$$Clearly, $a = 15$

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good job ,in math stackexchange there are very few questions that 12 years child can deal with. –  noname1014 Sep 15 '12 at 17:05
    
Thank you very much! This was comparatively an easy problem, thus making me have a go at it. –  Parth Kohli Sep 15 '12 at 17:12
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