Question 825010
Both pipes were used for 10 hours, and only pipe 2 was used for some unknown amount of time afterward.  The amount of tank filled was 1.  Let x = time in hours after the first 10 minutess.


First period:  p1 and p2 together for 10 minutes.
Second period:  p2 for x minutes.
Total Time:  1 tank.


Use the rate information as tanks per time.
p1 rate is 1/40 tanks per minute.
p2 rate is 1/60 tanks per minute
p1 and p2 together rate is {{{1/40+1/60=(3+2)/120=5/120=highlight_green(1/24)}}} tanks per minute.


You have from the key uniform rate idea, R*t=j meaning rate time time equals the amount of job.  Specific to our example,  {{{highlight((1/24)10+(1/60)x=1)}}}.
SOLVE FOR x.