Math question help!!!

<p>P and M can do a job in 2 hours. When P works alone, he can do 5 jobs in 15 hours. How many jobs can M do in 12 hours, alone?</p>

<p>***I believe that the answer is 6 jobs, but the answer sheet says its 2 jobs.</p>


<p>P does 5 jobs in 15 hours. That's 1 job in 3 hours or 1/3 job in one hour.</p>

<p>So in 2 hours, P does 2/3 job. M must have done the remaining 1/3 job in the two hours.</p>

<p>So M needs 6 hours to do 1 job. [Could that be the 6 you solved for?]
In 12 hours, he can do 2 jobs.</p>

<p>Another way to look at it, if you don't want to deal with fractions:</p>

<p>P alone can do 5 jobs in 15 hours, or 1 per 3 hours. That means P can do 4 jobs alone in 12 hours.</p>

<p>P and M together can do 1 job in 2 hours, so they can do 6 jobs total in 12 hours (that could also be the 6 you solved for).</p>

<p>In those 12 hours, if they do 6 jobs together, and P can do 4 in that time, it means M can do the remaining 2 jobs.</p>

<p>Same answer, but a different way to get there, that might be easier as it doesn't involve any fractions.</p>

Yes, I think I've solve for the hr, not the job. Thanks for the clarification!</p>

I didn't think of solving it your way. I guess I've learnt another way to tackle it. Thanks!</p>

<p>I also prefer CTScout's solution! I should have noticed that they asked for how many jobs could be done in 12 hours -- that's a weird thing to ask for. The more traditional question would have been: "How long does it take M to do the job?" -- that is so expected that you answered it! But when an SAT question asks for something unusual, there is often an easier path to get to it.</p>