Faucet a can fill a water cooler 8 minutes. faucet b can fill the same cooler in 12 minutes. how long will it take both faucets together to fill the water cooler?

This is a work problem. We can use theories on ratios and proportion in order to solve this. We do as follows:

Faucet A = 8 minutes to fill
Faucet B = 12 minutes to fill

1/8 + 1/12 = 1/x

let x represent the time it takes for both to fill the cooler

x = 4.8 minutes for  both to fill the cooler