30) A special roulette wheel has seven equally likely outcomes: 0, 1, 2, 3, 4, 5, 6. If you bet that an odd number comes up, you win or lose $10 according to whether or not that event occurs. If X denotes your ‘net’ gain, X=10 if we see 1, 3, or 5, and X = -10 otherwise. Suppose that you play this game 400 times. Let Y be your net gain after these 400 plays. The mean (expectation) and standard deviation of Y are, respectively (accurate to the number of figures shown):(adsbygoogle = window.adsbygoogle || []).push({});

A) -270; 198

B) -571; 198

C) -270; 988

D) -571; 988

E) none of the other answers displayed

I can get the mean (-571), but for the standard deviation, I only get the answer (apparently 198) when I use the formula:

sigma² _ new = b * sigma²_old

When the formula SHOULD use b², instead of just b.

(Im using sigma² = Sum((x_i-u)²*p) to get the original variance.)

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# Homework Help: Statistics question

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