When Blanca puts the stopper in place and the faucet running, the bathtub can be filled in 16 minuets. When she turns the faucet off and rem

Since the bathtub can be filled in 16 minutes, the rate is 1 bathtub / 16 minutes  or  1/16.

Since the bathtub can be emptied in 20 minutes, the rate is -1 bathtub / 20 minutes  or  -1/20.

Let  n  be the number of minutes.  The point is to get 1 full bathtub  =  1.

Filling + Emptying  =  1 Bathtub

(1/16)n  -  (1/20)n  =  1

Multiply each term by 320:

320(1/16)n - 320(1/20)n  =  320(1)

    20n - 16n  =  320

            4n  =  320

--->   n  =  80 minutes

Are these questions serious......

People are turning math into a joke its not my fault :(

good job geno! :)

Thanks Geno,

I always like these questions.   I have to think EVERY time.     

Here's another way to do this:

Each minute, the fractional amount that the tub is being filled = [1/16 - 1/20] = [20 - 16 / 320]  = 4/320

Now.....invert the fraction  =  320 / 4   = 80 minutes .....and that's how long it takes to fill the tub....