# Thread: Help please! I think this is to do with Distributions?

1. ## Help please! I think this is to do with Distributions?

Heya! =]

Two weeks of holidays has taken a toll on what I learnt about distributions. Could you guys please help me with a question? =]

This is the question I need help with:

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Two classes did the same test, which was out of 30 marks. The scroes for the two classes are shown below:

Class 1: 3, 4, 6, 6, 7, 11, 13, 16, 17, 18, 18, 19, 19, 20, 20, 21, 21, 21, 23

Class 2: 7, 8, 12, 13, 13, 14, 15, 15, 16, 17, 18, 18, 20, 20, 21, 21, 22, 23, 24, 26, 27, 29, 30

From Class 1, Alexander was one of the scores of 21. From Class 2, Alexandra was the person who scored 23.

Which of these two students can claim to have done better, in comparion to the rest of their class?

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I know I'm supposed to use a mean somewhere in it. So, here's the mean calculated out...

Class 1's mean: 14.89

Class 2's mean: 18.65

But what should I do with it now? =[

2. Originally Posted by Hikaru
Heya! =]

Two weeks of holidays has taken a toll on what I learnt about distributions. Could you guys please help me with a question? =]

This is the question I need help with:

----

Two classes did the same test, which was out of 30 marks. The scroes for the two classes are shown below:

Class 1: 3, 4, 6, 6, 7, 11, 13, 16, 17, 18, 18, 19, 19, 20, 20, 21, 21, 21, 23

Class 2: 7, 8, 12, 13, 13, 14, 15, 15, 16, 17, 18, 18, 20, 20, 21, 21, 22, 23, 24, 26, 27, 29, 30

From Class 1, Alexander was one of the scores of 21. From Class 2, Alexandra was the person who scored 23.

Which of these two students can claim to have done better, in comparion to the rest of their class?

-----

I know I'm supposed to use a mean somewhere in it. So, here's the mean calculated out...

Class 1's mean: 14.89

Class 2's mean: 18.65

But what should I do with it now? =[

You could assume that for each class the distribution of scores follows a normal curve. You can estimate the mean and standard deviation in each case from the data ......

Then calculate Pr(X1 > 21) and Pr(X2 > 23) ......

3. Originally Posted by mr fantastic
You could assume that for each class the distribution of scores follows a normal curve. You can estimate the mean and standard deviation in each case from the data ......

Then calculate Pr(X1 > 21) and Pr(X2 > 23) ......
Ah, yes! That's right! The whole standard Deviation idea is coming back to me!

However, what do you mean by PR?

4. Originally Posted by Hikaru
Ah, yes! That's right! The whole standard Deviation idea is coming back to me!

However, what do you mean by PR?
Pr(X1 > 21) means the probability that the score in class 1 is greater than 21 etc.

5. Originally Posted by mr fantastic
Pr(X1 > 21) means the probability that the score in class 1 is greater than 21 etc.
Wait, it became confusing again. =[

I tried getting the standard deviation but I keep on ending up with 4. That's not right... How do I work it out? =[

6. Originally Posted by Hikaru
Wait, it became confusing again. =[

I tried getting the standard deviation but I keep on ending up with 4. That's not right... How do I work it out? =[
There is a formula for computing standard deviation. See for example Standard deviation - Wikipedia, the free encyclopedia

Alternatively, most scientific and all graphics calculators can also calculate it once you've entered the data. You can even do it on-line: Maths Calculator - Standard Deviation - Calculation, calculate standard deviation, variance

So try one of the above - I don't do drudge work (I have slaves for that).