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Chapter 7, Practice question 7.3

C

Cam Bridger

Keen member
When looking at the solution I don't understand how we go from P(Xbar - Ybar > 3) to P(Z > 0.564)

I believe we're doing (3 - 0) / (sqrt(28.26) / sqrt(n)) = 0.564? This gives n = 1 which doesn't make sense to me, could someone explain please?
 
Hi Cam
It is (3-0)/sqrt(28.26), there is no sqrt(sigma^2/n) here, you have the distribution for Xbar and Ybar, and for (Xbar-Ybar) this is another normal mean 0 and the variance is the sum of the two variances for Xbar and Ybar, giving you the 28.26, which you then square root for the denominator when standardising.
 
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