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Three numbers in arithmetic progression have common difference 6 and mean 20. Find their standard deviation.

Competition practiceStatistics

A6
B $43$
C $6$
D $26$

Step-by-Step Solution

The numbers are 14, 20, 26. Variance

= \frac{36 + 0 + 36}{3} = 24

, SD

= 24 = 26

. (6 is just the common difference.)

Answer: D)

26

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