2 pipes are used to fill pool. 1st pipe can fill the pool 6 hrs alone. two pipes can fill in 3 hrs less time than 2nd pipe. how long it will take for 2nd pipe?

Question

kindly help meeee. I'm reviewing this for my college entrance test. please help

Answer 1

Let x = time it takes the second pipe to fill the pool

 

Then, x-3 = time it takes both pipes together to fill the pool

 

1/6 = portion of pool filled by first pipe in one hour

 

1/x = portion of pool filled by second pipe in one hour

 

1/(x-3) = portion of pool filled by both pipes in one hour

 

So, 1/6 + 1/x = 1/(x-3)

 

Multiply by the LCD, 6x(x-3):

 

   x(x-3) + 6(x-3) = 6x

 

   x² - 3x + 6x - 18 = 6x

 

   x² - 3x - 18 = 0

 

   (x-6)(x+3) = 0

 

   x = 6 or x = -3

 

Since x can't be negative, x = 6 hours