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Of all of the individuals who develop a certain rash, suppose the mean recovery time for individuals who do not use any form of treatment is 30 days with standard deviation equal to 8. A pharmaceutical company manufacturing a certain cream wishes to determine whether the cream shortens, extends, or has no effect on the recovery time. The company chooses a random sample of 100 individuals who have used the cream, and determines that the mean recovery time for these individuals was 28.5 days. Does the cream have any effect

Sagot :

Answer:

z(s) is in the rejection  region. We reject  H₀. We dont have enought evidence to support that the cream has effect over the recovery time

Step-by-step explanation:

Sample information:

Size     n = 100

mean   x = 28,5

Population information

μ₀  =  30

Standard deviation  σ   = 8

Test Hypothesis

Null Hypothesis          H₀                x =  μ₀

Alternative Hypothesis   Hₐ           x <  μ₀

We assume CI = 95 %   then α = 5 %    α = 0,05

As the alternative hypothesis suggest we should develop a one tail-test on the left ( we need to find out if the cream have any effect on the rash), effects on the rash could be measured as days of recovery

A z(c) for 0,05 from z-table is:  z(c) = - 1,64

z(s) = ( x - μ₀ ) / σ/√n

z(s) = ( 28,5 - 30 ) / 8/√100

z(s) = - 1,5 * 10 / 8

z(s) =  - 1,875

Comparing z(s)  and z(c)

|z(s)| < |z(c)|        1,875  > 1,64

z(s) is in the rejection  region. We reject  H₀. We dont have enought evidence to support that the cream has effect over the recovery time

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