.
Three machines are filling water bottles. The machines can fill the daily quota of water bottles in 90 h, 99 h, and 110 h, respectively.
How long would it take to fill the daily quota of water bottles with all three machines working?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The first machine can fill of the daily quota of bottles in one hour (in each hour). It is its rate of work.
The second machine can fill of the daily quota of bottles in one hour (in each hour). It is its rate of work.
The third machine can fill of the daily quota of bottles in one hour (in each hour). It is its rate of work.
If all three machines works simultaneously, they fill
= = = =
of the daily quota of bottles in one hour (in each hour).
Hence, it will take hours for the three machine to fill the daily quota of bottles working simultaneously.