hellokym Posts: 1, Reputation: 1 New Member #1 Dec 12, 2007, 02:54 PM
Probability of sample mean?
download time was normally distributed, with a standard deviation of 0.2 second. If you select a
a. What is the probability that the sample mean is less than 0.75 seconds?
b. What is the probability that the sample mean is between 0.70 and 0.90 seconds?
 Ketan3 Posts: 1, Reputation: 1 New Member #2 Oct 24, 2009, 11:14 AM
(.8-.75)/.2=.25

+((.7-.75)/.2)=.25

((-.7-.75)/.2)=-7.25
 galactus Posts: 2,271, Reputation: 282 Ultra Member #3 Oct 24, 2009, 12:35 PM
download time was normally distributed, with a standard deviation of 0.2 second. If you select a

a. What is the probability that the sample mean is less than 0.75 seconds?
$z=\frac{(x-{\mu})\sqrt{n}}{\sigma}=\frac{(.75-.8)\sqrt{30}}{.2}=-1.37$

Look it up in the z table.

b. What is the probability that the sample mean is between 0.70 and 0.90 seconds?
$z=\frac{(.7-.8)\sqrt{30}}{.2}=-2.74; \;\ z=\frac{(.9-.8)\sqrt{30}}{.2}=2.74$

Look them up in the z table and subtract.
 Ositadima Posts: 1, Reputation: 1 New Member #4 Jul 9, 2010, 04:33 PM
Galactus your solution has really helped me to regain my balance on this problem. I somehow got lost and your solution rebounced me back. Thank you for taking your time to contribute mathematically. It surely does not come so easy. Keep on with the good work and always make sure that you answer correctly.

Thanks again,

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