Question 139424
a task ( painting, pool filling, etc.) that is completed by multiple "inputs" (people, pipes, etc.)
__ is a whole made up of fractions __ the fractions sum to 1 (the whole)


an input's fraction is found by dividing the combined time by the individual time
__ e.g. if A can do a job in 5 hrs, but only takes 3 hours when working with B;
__ A does 3/5 of the job and B does the other 2/5
__ B does 2/5 in 3 hrs, so it would take him 3/(2/5) or 15/2 hr alone



painting:  let x="time together" __ (x/4)+(x/6)=1
__ multiplying by 12 __ 3x+2x=12 __ 5x=12 __ x=12/5=2.4=2hr 24min


filling:  letx="time together" __ (x/30)+(x/45)+(x/90)=1
__ multiplying by 90 __ 3x+2x+x=90 __ 6x=90 __ x=15



good luck with retraining