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The first of two samples has 100 items with mean 15 and standard deviation 3. The combined group of 250 items has mean 15.6 and standard deviation sqrt(1344)/10. Find the standard deviation of the second sample (which has 150 items).

1. 8
2. 6
3. 4
4. 5

Correct answer: 4

Solution

Setting up the combined variance equation with n1=100, n2=150, sigma1=3, d1=-0.6, d2=0.4, and combined variance=13.44 gives sigma2² = 25, so sigma2 = 5.

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