Another Word rationsl equation again, need help

[bradycat]

Hello,
A tank can be filled by one of two pipes in 12.00 h and by the other of the two in 1.00 h. The same tank can be emptied by a drain pipe in 10.5h. If all three pipes are open, how long will it take to fill the tank.

Answer in time?
I know it's 1/12 + 1/1 - 1/10.5 = Need to find the time it takes to fill the tank.

I have no clue on subtracing a fraction with a decimal if you have to have the LCD to clear the fractions???

Please help thanks - PLEASE EXPLAIN how it's calculated.
Joanne

 

[Denis]

I know it's 1/12 + 1/1 - 1/10.5 = Need to find the time it takes to fill the tank.
I have no clue on subtracing a fraction with a decimal if you have to have the LCD to clear the fractions???

1/ 10.5 = 2 / 21 ... POUFF! the decimal vanished...

 

[bradycat]

Hi Denis,
So do I multiply them all by 2/2 for the other 2. I don't think it's just to one correct??
J

 

[wjm11]

So do I multiply them all by 2/2 for the other 2. I don't think it's just to one correct??

It's always okay to multiply any individual term by "1" (and 2/2 is just another way to say 1) because it doesn't change the value of that term -- it just changes the way it looks.