Two pipes A and C can fill a tank in 10 hours and 15 hours respectively. If A is open all the time and C is open for 30 minutes, then find the time needed for the tank to be filled.
A$$9\frac13$ hours$
B$$8\frac43$ hours$
C$$9\frac23$ hours$
D$$8\frac23$ hours$
Answer:
$$9\frac23$ hours$