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Topic: [ap-stat] RE: YMS Test 7C
Replies: 0

 Corey Andreasen Posts: 5,070 Registered: 12/6/04
[ap-stat] RE: YMS Test 7C
Posted: Dec 9, 2004 7:12 PM

If you multiply a set of numbers (with mean mu and standard deviation s) by a, the new mean is a*mu. The new sd is a*s. New var = (new sd)^2 = a^2 * (s)^2 = a^2 * (orig var). In this case, a = .3, so a^2 = .09, and .09*50 = 4.5.

Corey

-----Original Message-----
From: gds901 [<a href="mailto://gds901@email.midflorida.com]">mailto://gds901@email.midflorida.com]</a>
Sent: Thu 12/9/2004 5:10 PM
To: for Teachers of AP Statistics
Subject: [ap-stat] YMS Test 7C

After 14 hurricane days this fall and taking on too many new duties this
year, my brain finally went on vacation today. I'm looking for a little
help

Cans of soft drinks cost \$0.30 in a certain vending machine. What is
the expected value and variance of daily revenue (Y) from the machine,
if X, the number of cans sold per day has E(X) = 125 and Var(X) = 50?

a) E(Y) = 37.5, Var(Y) = 50
b) E(Y) = 37.5, Var(Y) = 4.5
c) E(Y) = 37.5, Var(Y) = 15
d) E(Y) = 37.5, Var(Y) = 15
e) E(Y) = 125, Var(Y) = 4.5

I did use a probably suspect process of elimination to come up with the
key's answer "B". I didn't have trouble with E(Y), but I need help with
Var(Y).

Thanks

Jan Smith
Auburndale High School
Auburndale, FL

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