Posted by **Nora** on Monday, October 31, 2011 at 10:45pm.

The number of cases for a disease has reduced by half every 10 years:

1970 - 21,168

1980 - 10,584

1990 - 5,292

Assume N is the number of reported cases t years after 1970. Which is a good model for N(t)?

a) 21,168 (2)^t

b) 21,168 (1/2)^t

c) 21,168 (1/2)^t/10

d) 21,168 (2)^t/10

- math -
**Steve**, Tuesday, November 1, 2011 at 11:00am
You need t/10, since the number is halved every 10 years.

Since it's halved, that's (1/2)^(t/10)

So, C

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