One pipe can fill one cistern in 20 hours and another pipe can fill one cistern in 30 hours. How long will it take to fill one cistern if both pipes are used?
Just take the amount of the total job that each pipe can do in one hour, 1/20 and 1/30, respectively......add them and take the reciprocal.......this is the time - in hours - to complete the job
Just take the amount of the total job that each pipe can do in one hour, 1/20 and 1/30, respectively......add them and take the reciprocal.......this is the time - in hours - to complete the job
