Posted by NEED HELP NOW!! on .
The first of three pipes fills a tank in 12 minutes and a second pipe in 10 minutes. If both these pipes and also a third pipe are open the tank is filled in 4 min. How many minutes will the third pipe alone require to fill the tank?
My teacher told me to use a chart and an equation for this question. so any help i can get would be great. I'm sorta clueless of how to label the chart, also! thanks!

Algebra 1 
Steve,
just add up the amount each pipe does in one minute. The result must equal how much is done by everyone in 1 minute:
1/x + 1/12 + 1/10 = 1/4
x = 15