Math
posted by Rayhan .
The population of a city has been decreasing exponentially since 1990. In 1990, the population was 1,000,000. In 2010, the population was 560,000. If t represents time in years since 1990, which of the following equations best models the decay of the population?
1.
y = 1,000,000(0.98)t
2.
y = 560,000(0.98)t
3.
y = 1,000,000(1.02)t
4.
y = 560,000(1.02)t

Math 
Damon
think !
1. It starts in 1990 at 1,000,000
2. it DECREASES
and you meant to the POWER t, not times t
a k^t not a k t
to check
at 2010, t = 20 years
y = 1,000,000* .98^20 ? 
Math 
Reiny
First of all looking at your choices, only 1. and 2. are logical, the other two would show an increase not a decrease, so ....
let the rate be r
560000 = 1000000 r^10
.56 = r^10
take 10th root of both sides using your calculator
.56^(1/10) = r
r = .94367..
so y = 560000(.94)^t would be it using 2 decimals like all their answers
I don't see that choice!!!
check:
.94367^10 = .560017...
.560017...(1000000) = 560,017 close enough
My answer is correct
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