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A variable $x$ has standard deviation 7. Find the standard deviation of $y = 4 - 3 x$ .

Competition practiceStatistics

A63
B21
C−21
D17

Step-by-Step Solution

SD(a +

b x) = ∣ b ∣ \times

SD

(x) = 3 \times 7 = 21

. The 4 has no effect and an SD is never negative. (63 squares the 3 as for a variance.)

Answer: B) 21

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