SOLUTION: I've tried to figure out what to use but for some reason it hasnt come to me. Please help me solve this equation: Two pipes are used to fill a water storage tank. The first pipe

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Question 154284: I've tried to figure out what to use but for some reason it hasnt come to me.
Please help me solve this equation: Two pipes are used to fill a water storage tank. The first pipe can fill the tank in 4 hours, and the two pipes together can fill the tank in 2 hours less time than the second pipe alone. How long would it take for the second pipe to fill the tank?
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
let s="second pipe alone"

each pipe fills some fraction of the tank
__ the fraction is (combined time)/(time alone)
__ the fractions add to the whole, 1

eg. if you can do a task in 6 hrs; when you work in a group that takes 2 hrs, you do 1/3 of the task (2/6)

(s-2)/4 + (s-2)/s = 1 __ multiplying by 4s __ s^2-2s+4s-8=4s

subtracting 4s __ s^2-2s-8=0 __ factoring __ (s-4)(s+2)=0

s-4=0 __ s=4 __ same as 1st pipe

s+2=0 __ s=-2 __ negative value not realistic