A tank can be filled by pipe X in 2 hours and pipe Y in 6 hours. At 10...
Suppose the capacity of tank = 6 units (LCM of 2 and 6)
⇒ Efficiency of X = 6/2 = 3 and Efficiency of Y = 6/6 = 1
Pipe X was opened at 10 am and pipe Y is opened at 11 am
Units of water filled by X in 1 hour (10 a.m. to 11 a.m.) = 3 units
⇒ Remaining units of water to be filled = 6 - 3 = 3 units
⇒ Time taken by (X + Y) to fill the remaining tank = ¾ hours = 45 minutes
∴ Tank will get filled at 11:45 a.m.
View all questions of this test
A tank can be filled by pipe X in 2 hours and pipe Y in 6 hours. At 10...
Solution:
Let's assume that the capacity of the tank is 'C'.
Pipe X can fill the tank in 2 hours.
∴ In 1 hour, pipe X can fill 1/2 of the tank.
Pipe Y can fill the tank in 6 hours.
∴ In 1 hour, pipe Y can fill 1/6 of the tank.
Now, let's calculate the amount of water filled in the tank by pipe X in 1 hour, from 10 a.m. to 11 a.m. (when pipe Y is opened).
Time taken by pipe X from 10 a.m. to 11 a.m. = 1 hour
∴ Amount of water filled by pipe X in 1 hour = 1/2 of the tank
Now, both pipes X and Y are working together.
Combined rate of work = Rate of work of pipe X + Rate of work of pipe Y
= 1/2 + 1/6
= 2/3
∴ In 1 hour, both pipes working together can fill 2/3 of the tank.
Let's assume that the tank gets filled completely after t hours.
Amount of water filled by pipe X from 10 a.m. to t hours = (t-1) × 1/2 of the tank
Amount of water filled by pipe Y from 11 a.m. to t hours = (t-11) × 1/6 of the tank
As both pipes are working together, the sum of the above two amounts should be equal to the capacity of the tank 'C'.
∴ (t-1) × 1/2 + (t-11) × 1/6 = C
Simplifying the above equation, we get:
3t - 23 = 6C
∴ t = (6C + 23)/3
Now, we know that the tank gets filled completely. Hence, C is equal to 1.
∴ t = (6+23)/3
= 29/3 hours
= 9 hours and 40 minutes
Therefore, the tank will be filled at 11:00 a.m. + 9 hours and 40 minutes = 8:40 p.m.
But the question asks for the time at which pipe Y is opened.
Time taken from 11 a.m. to 8:40 p.m. = 9 hours and 40 minutes
∴ The tank will be filled at 11:00 a.m. + 9 hours and 40 minutes = 8:40 p.m.
Therefore, the correct answer is option (c) 11:45 a.m.