If a sample of 25 canned goods is selected, what is the probability that the mean of the sample will be larger than 20 mg?
Let XXX be the mean sample: X∼N(μ=25, σ2=152)X\sim N\left(\mu =25,\:\sigma ^2=15^2\right)X∼N(μ=25,σ2=152) Then,
Z=x−μσ∼ N(0,1)Z=\frac{x-\mu }{\sigma }\sim \:N\left(0,1\right)Z=σx−μ∼N(0,1)
The probability that the mean of the sample will be larger than 20mg is:
X∼N(μ=25, σ2=152)X\sim N\left(\mu =25,\:\sigma ^2=15^2\right)X∼N(μ=25,σ2=152)
=1−P(Z≤25−2015)≈1−P(Z≤0.3333)=1-P\left(Z\le \frac{25-20}{15}\right)\approx 1-P\left(Z\le 0.3333\right)=1−P(Z≤1525−20)≈1−P(Z≤0.3333)
≈0.3694\approx 0.3694≈0.3694
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