Algebra 1

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

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.

asked by Brittany
  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

    posted by Reiny
  2. So is #1 wrong?

    posted by Brittany
  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.

    posted by Brittany
  4. amount = 4000(1.04)^3

    I get $ 4499.46

    posted by Reiny
  5. Thanks Reiny.

    posted by Brittany

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