>If using hose A, I can fill a drum in 20 minutes but if I am going to use hose B, I will only take 18 minutes. If I will use both (A & B), how many minutes will I spend to fill the drum?
>
>30 + 18 = 38; 38/2 = 19, 19/2 = 9.5 which is my answer. Is this correct?

Jess;

When I was an Electronics technician we had “short hand methods” to solve problems. A simple equation would render an approximate result satisfactory for the work at hand. Then I went to college to study Electronics Engineering and Physics, I was taught to calculate such things by attempting to remove all variables.

Rather than thinking in “two dimensions” we thought in 3. To solve the problem you stated would require an engineer to know the circular mil area of the hoses and the pressure vs. time (it may vary), the material the hose was made of and its wall diameter. You would end up with at least three pages of calculations. The result would be more accurate but of little interest to the “real world”! :)

Tom