# Simple maths problem, did I do it right?

• 10-20-2002
Zewu
Simple maths problem, did I do it right?
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?

Code:

```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```
• 10-20-2002
Sang-drax
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!
• 10-21-2002
golem
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:
• 10-21-2002
Zewu
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.