Question

A blood sample has 50,000 bacteria present. a drug fights the bacteria such that every hour the number of bacteria remaining, r(n), decreases by half. If r(n) is an exponential function of the number, n, of hours since the drug was taken, find the bacteria present four hours after administering the drug.

Answer 1

3125 bacteria

Explanation:

Let r(0) be the initial amount of bacteria. Every hour, r(n) decreases by half. So, after one our new value for r(n) = (1/2)r(0). After two hours, r(n') = (1/2)r(n) = (1/2)(1/2)r(0) = (1/2)²r(0).

After n hours, r(n) = (1/2)ⁿr(0)

So when n = 4 hours and r(0) = 50,000, then

r(4) = (1/2)⁴r(0)

r(4) = (1/2)⁴ × 50,000

r(4) = (1/16) × 50,000

r(4) = 3125

So, after 4 hours, we have 3125 bacteria present.