I am having trouble with a few questions....Wondering if you could help...My answers have the *** by them.....

Question

1. A lab is growing bacteria in a culture dish. The amount of bacteria in the dish doubles every 3 hours. Initially, there are 500 bacteria in the dish. How many are in the dish after 9 hours?

A. 4,500 bacteria.
B. 4,000 bacteria.
C. 1,500 bacteria. ***
D. 13,500 bacteria.

2. Determine if the number is written in scientific notation. If not, explain 32 x 10^4.

A. No; it is not written as a power of 10.
B. No; the first factor is not a number between 1 and 10.***
C. Yes; the number is written in scientific notation.

3. Determine if the number is written in scientific notation. If not, explain 2.01 x 10^-5.

A. No; it is not written as a power of 10.
B. No; the first factor is not a number between 1 and 10.***
C. Yes; the number is written in scientific notation.

Answer 1

#1, they double ever 3 hours, so
after 3 hours you would have 1000
after 6 hours you would have 2000
after 9 hours you would have 4000
or: number = 500(2^(t/3)) , plug in t = 9

#2, correct

#3,
2.01 certainly IS a number between 1 and 10
so C

Answer 2

So is #1 wrong?

Answer 3

Another question. An investment account earns 4% per year compounded annually. If the initial investment was $4,000.00, how much is in the account after 3 years? Round your answer to the nearest dollar.

Answer 4

amount = 4000(1.04)^3

I get $ 4499.46

Answer 5

Thanks Reiny.

Answer 6

Thanks for the help, I was struggling on the same ones