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View Full Version : Simple maths problem, did I do it right?



Zewu
10-20-2002, 11:49 AM
I had this problem on a test. I failed it there due to lack of time, but I still want to know if I can solve it. Did I do it right?



Pump 1 pumps up the oil in a tank in 24 H. Pump 2 pumps up the oil in 36 H. How many H does it take to pump up the oil if both of the pumps are working?




/----\
Work
/-------------\
/Capacity|H \
/-----------------\

After 100 units of work, the oil has been pumped up.

Work/Pump1 H = Pymp 1 Capacity
100/24 = 4,167

Work/Pump2 H = Pump 2 Capacity
100/36 = 2,778

Pump 1 Capacity+Pump 2 Capacity
4,167+2,778 = 6,945

Work/Capacity = H
100/6,945 ~= 14,4

4*0,6=2,4


Result: 14 H and 24 min

Sang-drax
10-20-2002, 01:01 PM
Let me see...

Tank volume : 1 v.u.

Pump1 speed : 1/24 v.u./h
Pump2 speed : 1/36 v.u./h

Total speed : 1/24 + 1/36 = 5/72 v.u./h

Combined time = (1 v.u.) / (5/72 v.u./h) = 14.4 h = 14 hours 24 min

Correct!

golem
10-21-2002, 07:37 AM
Yet another solution

V is the volume of tank

P1 pumps up V/24 oil per hour

P2 pumps up V/36 oil per hour

If they would work together they pumped up V/24 + V/36 oil per hour

They will work V/(V/24 + V/36) hours to make the tank full

that is V / (V * (36 + 24) / 36 * 24) = 36 * 24 / (36 + 24) =

14,4 hours = 14 h 24 min

Don't you have any tougher?:rolleyes:

Zewu
10-21-2002, 12:12 PM
Sorry, but I'm in grade 9 of our social democratic compulsory school. They don't want those who appear to have an easy time with, for example maths, to get their own tougher questions, test, teachers etc., as this would create an elite.