In the monthly payment formula M = Pr{1+r)". what value do you give rif the (1+r)" - 1
interest rate is 9.7%?
A. 0.0081
B. 0.0097
C. 0.81
D. 0.97
NUM

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:  

answer is b.

15

i got this one as well.