Question 986460
<pre>

PERSON   RATE
Peter    2/x
Henry    1/x
Joint    1/10

</pre>
Find Henry's rate first unless you want to take the unknown times from another viewpoint.


Note that x is not a rate; it is the time for Henry to do one whole job himself.


{{{2/x+1/x=1/10}}}
-
-
{{{3/x=1/10}}}
{{{x/3=10}}}
{{{x=30}}}-----time in days for Henry to do one job alone.


The practical sense is that Peter is twice as fast as Henry, so Peter can do the same one job alone in 15 days.