One pipe can fill a tank in 20 minutes while another takes 30 minutes to fill the same tank How long will it take the two pipes together to fill the tank?

Answer 1

The first pipe will fill one tank in 36 hours. Therefore in one hour it will fill 1/36 tanks. The second pipe will fill one tank in 45 hours. Hence in one hour it will fill 1/45 tanks. Between them, then, the two pipes will fill 1/36 + 1/45 tanks in an hour. This equals 5/180 + 4/180 = 9/180 = 1/20 tanks per hour. Hours per tank is just the reciprocal of tanks per hour, i.e. 1/[1/20] = 20 hours to jointly fill a tank. Incidentally, adding reciprocals and taking an overall reciprocal is a very commonly used trick. It is used to calculate net parallel resistance in electric circuits. Here, time to fill a tank (or resistance to tank-filling!) can be considered analogous to electrical resistance.

Answer 2

Consider Pipe A In 18 hrs, its filling the full tank = 1 (whole) In 1 hr, its filling 1/18th part of tank //ly, in 1 hr, Pipe B is filling 1/24th part of tank If both pipes are opened at the same time, then in 1 hr, part of the tank filled is (1/18) + (1/24) = 7/72 Therefore, time taken to fill the full tank = 1 / (7/72) = 72/7 hrs = 10.28 hrs

Answer 3

17:08.57 Let V equal the volume of the tank and let a, b and c represent the flow rates for pipes A, B and C respectively: V = 20a = 30b = 40c Express a and b in terms of c: a = 2c b = 4c/3 With all pipes opened on an empty tank, the net rate of filling (R) is: R = a + b - c Substituting for a and b in terms of c: R = 2c +4c/3 - c R = 7c/3 Dividing the volume by the fill rate will yield the time: t = V/R t = 40c/(7c/3) t = 120/7 t = 17.14 minutes or 17 minutes and 08.57 seconds

Answer 4

25 minutes, half the time for both and add them together.

Edited by Jebaston

If u think like that then its absolutely wrong!!!!

a single pipe can fill it in 20 seconds, then how come it will be 25 min for 2 pipes to fill the same tank?

1/20 of the tank will be filled in 1 min by pipe A

1/30 of the tank will be filled by pipe B in 1 min

combinig together

1/20 + 1/30 of the tank will be filled in 1 min by both Pipe A + B.

ie. 1/12 (add them together) of the tank will be filled in 1 min by both Pipe A + B.

=> in 12 min the entire tank will be filled!!!

:P