Question

You are a researcher studying the lifespan of a certain species of bacteria. A preliminary sample of 40 bacteria reveals a sample mean of ¯x=78 hours with a standard deviation of s=4 hours. You would like to estimate the mean lifespan for this species of bacteria to within a margin of error of 0.7 hours at a 90% level of confidence.

What sample size should you gather to achieve a 0.7 hour margin
of error? Round your answer *up* to the nearest whole
number.

n = ? bacteria

Answer #1

Solution :

Given that,

standard deviation =s = =4

Margin of error = E = 0.7

At 90% confidence level of z is

= 1 - 90%

= 1 - 0.90 =0.10

/2
= 0.05

Z/2
= Z0.05 = 1.645

sample size = n = [Z/2* / E] 2

n = ( 1.645 *4 /0.7 )2

n =88.36

Sample size = n =88 rounded

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