A $1700 computer is worth 70% of its value each year in how many years will the value of the computer be less than or equal to $100

Question

What equation do I use to solve this problem

Answer 1

1700*(0.7)^y=100 or less where y=# of years it takes

(0.7)^y=100/1700

(0.7)^y=1/17

log([0.7]^y)=log(1/17)

y*log(0.7)=log(1/17)

y=log(1/17)/log(0.7)

y=-1.2304489/-0.1549019

y=7.9≈8 years

1700*0.7=1190           1

1190*0.7=833             2

833*0.7=583.10          3

583.10*0.7=408.17     4

408.17*0.7=285.72     5

285.72*0.7=200          6

200*0.7=140              7

140*0.7=$98              8