7. | A tank is filled in 5 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank? | ||||||||||||||||||||||||||||||||||
Answer: Option C Explanation:
Suppose pipe A alone takes x hours to fill the tank.
x = 35 hrs. |
8. | Two pipes A and B together can fill a cistern in 4 hours. Had they been opened separately, then B would have taken 6 hours more than A to fill the cistern. How much time will be taken by A to fill the cistern separately? | ||||||||||||||||||||||
Answer: Option C Explanation:
Let the cistern be filled by pipe A alone in x hours. Then, pipe B will fill it in (x + 6) hours.
x^{2} – 2x – 24 = 0 (x -6)(x + 4) = 0 x = 6. [neglecting the negative value of x] |
9. | Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank? | |||||||||||||||||||||||||||
Answer: Option A Explanation:
Both pipes can fill the tank in 12 minutes. |
10. | Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank? | |||||||||||||||||||||||||||||||||||||||||||||||||
Answer: Option D Explanation:
The tank will be full in (4 min. + 10 min. + 40 sec.) = 14 min. 40 sec. |