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ANTONII [103]
3 years ago
13

A bacterial culture starts with 400 bacteria and grows at a rate proportional to its size. After 2 hours there will be 800 bacte

ria.
1) Express the population, P(t) after t hours as a function of t
2) Using your equation from above, what will the population be after 8 hours?
3) Using your equation from above, after how many hours will the population reach 2270 bacteria?
Mathematics
1 answer:
kotykmax [81]3 years ago
7 0

Answer:

  1. P(t) = 400×2^(t/2)
  2. 6400
  3. 5.0

Step-by-step explanation:

The wording "a rate proportional to its size" is an indication that growth (or decay) is exponential.

1) For many problems involving exponential growth, I like to use the numbers given in the problem statement as follows.

  population = (initial population) × (growth factor)^(t/(growth period))

where the "growth period" is the period of time in which the population is multiplied by the "growth factor".

Here, we're given ...

  (initial population) = 400

  (growth factor) = 800/400 = 2

  (growth period) = 2 . . . . hours

So, our population function can be written as ...

  P(t) = 400×2^(t/2)

__

2) Putting t=8 into the formula, we get ...

  P(8) = 400×2^(8/2) = 400×16 = 6400

After 8 hours, the population will be 6400.

__

3) Fill in the given number and solve for t.

  2270 = 400×2^(t/2)

  2270/400 = 2^(t/2)

Taking logs, we have ...

  log(227/40) = (t/2)log(2)

  t = 2×log(227/40)/log(2) ≈ 5.009

After 5.0 hours, the population will reach 2270.

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Soloha48 [4]

Answer:

383

Step-by-step explanation:

Let dryer be d.

(d + 92) + d = 858

2d + 92 = 858

      -92 =  -92

---------------------

    2d = 766

    ----    ------

     2        2

       d = 383

The dryer is $383

Hope this helped.

3 0
2 years ago
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Of the 150 students that attended the science camp, 82 were sixth graders. Marco says that less than half of the campers were si
erastovalidia [21]

Answer:

Incorrect

Step-by-step explanation:

150 students are 100%,

82 students are x%

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3 years ago
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A state legislator wants to determine whether his voters' performance rating (0 - 100) has changed from last year to this year.
ra1l [238]

Answer:

Step 1 of 4

Point estimate for the population mean of the paired differences = -8.2

Step 2 of 4

Sample standard deviation of the paired differences = 16.116244

Step 3 of 4

Margin of Error = ±9.326419

Step 4 of 4

90% Confidence interval = (-17.5, 1.1)

Step-by-step explanation:

The ratings from last year and this year are given in table as

Rating (last year) | x1 | 87 67 68 75 59 60 50 41 75 72

Rating (this year) | x2| 85 52 51 53 50 52 80 44 48 57

Difference | x2 - x1 | -2 -15 -17 -22 -9 -8 30 3 -27 -15

Step 1 of 4

Mean = (Σx)/N = (-82/10) = -8.2 to 1 d.p.

Step 2 of 4

Standard deviation for the sample

= √{[Σ(x - xbar)²]/(N-1)} = 16.116244392951 = 16.116244 to 6 d.p.

Step 3 of 4

Confidence Interval for the population mean is basically an interval of range of values where the true population mean can be found with a certain level of confidence.

Mathematically,

Confidence Interval = (Sample mean) ± (Margin of error)

Sample Mean = -8.2

Margin of Error is the width of the confidence interval about the mean.

It is given mathematically as,

Margin of Error = (Critical value) × (standard Error of the mean)

Critical value will be obtained using the t-distribution. This is because there is no information provided for the population standard deviation.

To find the critical value from the t-tables, we first find the degree of freedom and the significance level.

Degree of freedom = df = n - 1 = 10 - 1 = 9.

Significance level for 90% confidence interval

= (100% - 90%)/2 = 5% = 0.05

t (0.05, 9) = 1.83 (from the t-tables)

Standard error of the mean = σₓ = (σ/√n)

σ = standard deviation of the sample = 16.116244

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σₓ = (16.116244/√10) = 5.0964038367

Margin of Error = (Critical value) × (standard Error of the mean) = 1.83 × 5.0964038367 = 9.3264190212 = 9.326419 to 6 d.p.

Step 4 of 4

90% Confidence Interval = (Sample mean) ± (Margin of Error)

CI = -8.2 ± (9.326419)

90% CI = (-17.5264190212, 1.1264190212)

90% Confidence interval = (-17.5, 1.1)

Hope this Helps!!!

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fredd [130]

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__________

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Answer:

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Step-by-step explanation:

x = -20/4 = -5

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