one pipe can fill a tank in 90 minutes a second pipe can fill the tank in 60 minutes how long will it take to fill the tank if both pipes are

assuming your incomplete sentence is

"... how long will it take to fill the tank if both pipes are open "

rate of first = 1/90
rate of 2nd = 1/60
combined rate = 1/90+1/60 = 1/36

time at combined rate = 1/(1/36) = 36 minutes

To find out how long it will take to fill the tank if both pipes are used together, we need to calculate their combined rate of filling the tank.

Let's start by determining the individual rates at which each pipe can fill the tank.

For the first pipe, we are given that it can fill the tank in 90 minutes. Therefore, the rate at which this pipe fills the tank is 1 tank per 90 minutes, or 1/90 tanks per minute.

For the second pipe, we are given that it can fill the tank in 60 minutes. Therefore, the rate at which this pipe fills the tank is 1 tank per 60 minutes, or 1/60 tanks per minute.

Now, let's add the rates of both pipes to get the combined rate when they are used together.

Combined rate = Rate of first pipe + Rate of second pipe
= 1/90 tanks per minute + 1/60 tanks per minute

To add these fractions, we need to find a common denominator. The least common multiple of 90 and 60 is 180. Therefore:

Combined rate = (1/90) + (1/60)
= (2/180) + (3/180)
= 5/180 tanks per minute

Now that we have the combined rate at which both pipes fill the tank, we can find the time it will take to fill the tank by taking the reciprocal of the combined rate.

Time to fill tank = 1 / Combined rate
= 1 / (5/180)
= 180/5
= 36 minutes

Therefore, it will take 36 minutes to fill the tank if both pipes are used together.