Question 154284
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