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Group A has 50 values with mean 60 and SD 8; group B has 50 values with mean 70 and SD 6. What is the SD of the combined 100 values?

Competition practiceStatistics

A7
B7.07
C5
D8.66

Step-by-Step Solution

Combined mean

= 65

, so

d_{1} = - 5, d_{2} = 5

. Variance

= \frac{50 ( 64 + 25 ) + 50 ( 36 + 25 )}{100} = 75

; SD

= 75 \approx 8.66

.

Answer: D) 8.66

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