On a map, the distance between two towns is 12 centimeters. If 3 centimeters represents 90 miles, what is the actual distance between the cities in miles?

1) 2/5

2) zero=0/1

3) zero=0/2

4) -4/5

5) undefined=3/0

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

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