You invest $55 at 10% compounded annually for 3 years. how much will your investment be worth in 3 years?

The investment would be worth $15.5

You multiply 55×.10×3=15.5

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 correct answer is c) 2.