Every hour of training raises the salary $ ? 10 1100 20 1200 30 1300

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times both sides by 2, times () by 8, add alile terms, move terms, add alike and caculate divide both sides by 3

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:  

b. is true. hope this . happy