A guard in a 20m tall watchtower spots a vehicle at an angle of depression oi 25 How far horizontally from the tower is the vehicle, to one decimal place? (​

Solution given:

height[p]=20m

angle of depression [a]=25°

base[b]=?

we have

Tan a=p/b

tan 25=20/b

b=20/tan25

b=42.89 or 43

the tower is 43m far from the vehicle .

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:  

16 would be your answer