Question

three pipes a b and c can fill a tank in 6 hours. after working at it together for 2 hours c is closed and a and b can fill it in 7 hours. the number of hours takes by c alone to fill the cistern is -

Answer 1

let A& B together take time = x hrs
C takes time=y hrs
1/x+1/y=1/6
2/x+2/y=7/x
2/y=5/x
x=5y/2
2/5y+1/y=1/6
7/5 y=1/6
y=42/5 days