8. the quotient of two
numbers subtracted from 20

step-by-step explanation:

is their an equation anywhere i can take a   look at it and see if i am right.

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:  

hi,

the area of abcd is 245.

3*24=230

4*94=1039

2*12=24

add all of them up, you get 2450