A does 1/2 of a piece of work in 3 1/2 hours B does 1/4 of the remainder in 1 1/2 hours and C then finishes the work in 5 1/4 hours. How long would it have taken the three working together to do the works

step-by-step explanation:

3 3 6, because in every triangle the longer side is always shorter than the sum of the other two

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

source:  

the answer is a. 72. but i cant answer with less than 20 characters so here's some random text talking about it.