🚀 go-pugleaf

In article <6tgc6c$rqg$1@readme.online.no>, "Marie M. Moltubakk"
<mamoltub@online.no> wrote:

> I'm not sure this is the right place to ask, but I will try anyways. I
> attend an upper secondary school, and my teacher has just given us this:
> 
> Someone has a bath tub, and it is to be filled with water. If you tap cold
> water, it takes 9 minutes to fill it. If you tap warm water, it takes 12
> minutes. How much time will it take if you use both warm and cold water?
> 
> In my opinion there are more than one solution to this, because it depends
> on the bath tub. (Are there one or two taps, does the water run in the same
> speed or twice as fast when both warm and cold water is on?)
> 

If you assume that turning one tap on or off does not affect the rate of
flow from the other tap, as is usual in these problems, then

the cold tap alone fills 1/9 of tub per minute, 
the hot tap alone fills 1/12 of the tub per minute,
together thy fill 1/9 + 1/12 = 7/36 of the tub per minute.

Thus it takes 36/7 minutes = 5 1/7 minutes to fill the tub.