The second pump pumps 1/8 of the pool per hour.
Together they pump 1/5+1/8 = 13/40 of the pool per hour.
In two hours working togethe they have emptied 2*(13/40)=13/20 of the
pool, leaving 7/20 to be emptied by the first pump alone at 1/5 of the pool
per hour. So it will take (7/20)/(1/5) hours to finish emptying the pool,
which is 7/4 hours = 1 hour 45 min.
(1) Is this question similar to math questions about working alone and working together?
I do it as shown above.(2) How do you set up an equation for such a question?