Question 38274
The normal equation for this kind of equation is
t/A + t/B = 1
where t is the time working together
A is the time it takes the first person working alone
B is the time it takes the second person working alone
and the 1 represents one whole job to do...
Now plug in and solve for B
20/45 + 20/B = 1
multiply all by 45B to clear fractions
20B + 900 = 45B
900 = 25B
B = 36 minutes