# find expected value, standard deviation, and probability

• May 7th 2009, 12:43 AM
jd254
find expected value, standard deviation, and probability
this is a homework help. I'm stumped as to which formula or chapter to look at. please show guidance. IM NOT ASKING FOR AN ANSWER, just guidance.

Q4. In a Gallup poll, 47% of the eligible women responding said that they would date a coworker. Suppose 350 employed women were selected at random.
a) What would be the expected value and standard deviation of the number of these women who would date a coworker?
b) What is the probability that at least 180 of them would date a coworker?

a) u = n*p = 380*0.47 = 178.6
s = square root ( n*p*q) = square root ( 380*0.47*0.53) = 9.7232

b) the "at least" is throwing me off. I have no idea how to start this.
• May 7th 2009, 03:31 AM
pickslides
If I have 10 pizzas and I eat "at least" 7 of them it means I have eaten 7, 8, 9 or 10 of them.

(Rofl)
• May 7th 2009, 03:32 AM
mr fantastic
Quote:

Originally Posted by jd254
this is a homework help. I'm stumped as to which formula or chapter to look at. please show guidance. IM NOT ASKING FOR AN ANSWER, just guidance.

Q4. In a Gallup poll, 47% of the eligible women responding said that they would date a coworker. Suppose 350 employed women were selected at random.
a) What would be the expected value and standard deviation of the number of these women who would date a coworker?
b) What is the probability that at least 180 of them would date a coworker?

a) u = n*p = 380*0.47 = 178.6
s = square root ( n*p*q) = square root ( 380*0.47*0.53) = 9.7232

b) the "at least" is throwing me off. I have no idea how to start this.

Calculate \$\displaystyle \Pr(X \geq 180)\$.
• May 7th 2009, 03:39 AM
jd254
do i use 180.5 due to correction for continuity?
• May 7th 2009, 03:52 AM
mr fantastic
Quote:

Originally Posted by jd254
do i use 180.5 due to correction for continuity?

No. Read this: Stats: Normal Approximation to Binomial