An inlet pipe can fill a water tank in 12 hours. An outlet pipe can drain the tank in 20 hours. If both pipes are mistakenly left open, how long will
it take to fill the tank?

Explanation:

Let's consider the tank's full capacity is 240 gallons. I'm picking this number because 12*20 = 240.

If the tank is 240 gallons, then the inlet pipe can fill it at a rate of 240/12 = 20 gallons per hour. Note after 12 hours, we have 12*20 = 240 gallons filled assuming the outlet pipe is sealed shut.

At the same time, the outlet pipe is draining at a rate of 240/20 = 12 gallons per hour. After 20 hours, the outlet pipe would drain out 12*20 = 240 gallons assuming the inlet pipe is not adding any water.

With the two pipes playing this tug-of-war battle, the inlet pipe ultimately wins because it's adding more gallons of water each hour, compared to the amount drained per hour. The net change is +20-12 = 8 gallons per hour.

This means it will take 240/8 = 30 hours to fill the tank with both pipes open.

Another approach:

The inlet pipe can fill the tank in 12 hours, so it gets 1/12 of the job done per hour. The outlet pipe drains the tank in 20 hours, so it gets 1/20 of the job done in one hour.

The net change is 1/12 - 1/20 = 5/60 - 3/60 = 2/60 = 1/30

This means that when both pipes are open, 1/30 of the job is done per hour. By "job", I mean "filling the tank".

If x is the number of hours needed to do one full job, then we can multiply that by the unit rate (1/30) and set the result equal to 1

(rate)*(time) = 1 job

(1/30)*x = 1

x = 30*1

x = 30

It takes 30 hours to do the job with both pipes open.

0.84 dang lotta people are looking for this lol or if you round up its 1 but the overall answer to that is 0.84

step-by-step explanation:

correct answer is b. 27/8

step-by-step explanation: