John works part time making bird houses. He is paid $4 for each bird house that he completes. One particular week, he made 20 bird houses. Find his gross income for the week.

320ft

step-by-step explanation:

120 divided by 3 equals 40

40 times 4=160

160 times 2=320

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:  

eight hundred an fifty one point four hundred and fifteen

800+50+1+.4+.01+.005