One pipe fills a storage pool in 20 hours. a second pipe fills the same pool in 15 hours. when a third pipe is added and all three are used to fill the pool, it takes only 6 hours. find how long it takes the third pipe to do the job.

We work in rates per hour so we have the equation:-

1/20 + 1/15 + 1/x = 1/6 where x is the time for the third pipe

1/x = 1/6 - 1/15 - 1/20 = 1/20

so x = 20

The answer is 20 hours.

x= -3 and

step-by-step explanation:

to find the roots of a cubic, use division or factoring to find the factors then set equal to 0. as this is a difference of cubes, it factors into

where a is the cube root of .

here   this is 27 and the cube root of 27 is 3. so we write using the form:

.

set each factor to 0 and solve for x.

x-3=0

x=3

the quadratic expression does not factor and must be solved using the quadratic formula.

where a = 1, b=3, and c=9

this cubic has two complex roots.