Question
Pipe 'C' alone takes 5 more hours to fill the tank than the time taken by pipe 'C' and pipe 'D' together. Find the approximate time taken by pipe 'C' to fill the tank alone, given that pipe 'D' alone can fill the tank in 20 hours.
Solution
ATQ,
Let t be the time taken by pipe C to fill the tank alone. Pipe D alone fills the tank in 20 hours. Together, C and D take [20t/(20+t)] hours It's given that: 
Multiply through by 20+t: t(20+t)=20t+5(20+t) Expand = t2=5t+100 Rearrange into a quadratic equation = t2−5t−100=0 Solve using the quadratic formula:- 
The time taken by pipe C alone to fill the tank is 12.81 hours.
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