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# Simple graph Watch

1. Just a simple question.

I have a fractional frequency curve (think its a normal distribution), where as x increases so does f up to a maximum and then decreases.

and then I have a cumulative frequency which is F, where I'm told F(x) = Integral f(x)

So why is the integral = cumulative freq? (I know the integral = area under graph so is it just the normal distribution split into infinite sections and then its the sum of the area of the sections?
2. Say there was a questionarre and the question was "what is your favourite number?"1 person says 1, 2 people say 2, 1 person says 3. You end up with a normal distribution curve when x =1, f(x)=1 , x=2 f(x)=2 x=3 f(x) = 1 . This is a really simple example. Now obviously total people = 4. You can also find that with the area. For x=1 the length=1 and height = 1 so area = 1. For x=2 the length = 1 and height = 2. For x=3 the length is = 1 and height = 1 so area = 1. Total area = 4.

Sorry if this is a bad explanation, don't know how to word it otherwise
3. The distances travelled to work D km, by the employees at a large company are normally distributed with D ˜ N (30, 8 squared)

(a) Find the upper quartile, Q3, of D.

(b) Write down the lower quartile, Q1, of D.

(c) An outlier is defined as any value of D such that D < 8.4 or D > 51.6
An employee is selected at random.
Find the probability that the distance travelled to work by this employee is an outlier.
______________________________ ___________________________

For (a) you do P (D < Q3) and make it equal to something that’s what someone told me! I was wondering why the sign was < and not > to find the P (D < Q3)?

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Updated: December 19, 2010
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