Probability homework, need help

derik72090

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Mar 20, 2013
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1
A survey was conducted to measure the height of men. In the survey, respondents were grouped by age. In the 20-29 age group, the heights were normally distributed, with a mean of 67.9 inches and a standard deviation of 4.0 inches. A study participant is randomly selected.
Find the probability that his height is more than 70 inches.

My work:
Given: Mean=67.9 S.D.=4.0 70-67.9/4.0=z=0.525
P(x>70)=P(z>0.525) (look on table, 0.5239 is closest # to 0.5250)
1-0.5239=0.4761
OR 1-0.5250=0.4750 may be right? Haven’t tried this way.

2nd question:

The scores on a Chemistry test are distributed normally with a mean of 56 and a standard deviation of 10.8. Because of the low average, the grades are curved so as to assign

7% A’s, 17% B’s, 52% C’s, 18% D’s, 6% F’s

What is the lowest possible C grade?

My work:
Given: Mean=56 S.D.=10.8
C-: Area to left= Ds and Fs=24%
0.2400 on table =z=-0.70
56-0.70(10.8)=48.44 pretty sure it said I got this one wrong too

Please help with this. I don't know what to do.
 
Pretty good work. Keep it up. You are very close.

Heights - The test value is above the mean. The test region is above the test value. MUST be less than 1/2.

Grades - It seems like you have it. Is 48.44 the Lowest C grade or the highest D grade? Are the scores whole numbers? Maybe 49 is the lowest C grade.
 
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