hot water fills a tub in 25 min. cold fills in 20. How long for both at same time?

Question

The hot water tap can fill a tub in 25 minutes. The cold water tap takes 20 mins to fill the same tub. How long would it take both taps open at the same time?

Answer 1

1/25 is the rate of hot water coming in

1/20 is the rate of cold water coming in

let x= minutes to fill the tub

 

then 

x/25+x/20=1

 its 1 on the right side, signifying that 100% of the tub is filled

multiply 100 on both sides

 

4x+5x=100

x=100/9

 

so it takes 11.1111minutes