Question 1078978
in an hour the janitor can clean 1/2 the building
with a helper they both can clean 1/1.25 of the building in an hour 
therefore, in 1 hour
(1/2)+(1/x)=1/1.25, where x is the number of hours the helper takes
multiply everything by 1.25 to get the right side equal to 1, 1 complete building.  This doesn't have to be done but then the answer is for 0.8 of the building and more work has to be done.
1.25/2+1.25/x=1
Now by 2x
1.25x+2.5=2x
0.75x=2.5
x=3.33 hours