# HELP - Normal distribution question

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#1
Q: Students' scores in a particular test follow a normal distribution with a mean of 39 and a standard deviation of 5.
What percentage of a class should score between 34 and 44 marks?
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#2
I did this in my calculator:
- lower bound = 34
- upper bound = 44
- standard deviation = 5
- mean = 39
I got 0.68268921, so I times my answer by 100 but when I put my answer in dr frost it's wrong? Maybe it's because I times it by 100 and put it in? I don't know what I did wrong
Last edited by GogetaORvegito?; 1 year ago
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1 year ago
#3
(Original post by GogetaORvegito?)
I did this in my calculator:
- lower bound = 34
- upper bound = 44
- standard deviation = 5
- mean = 39
I got 0.68268921, so I times my answer by 100 but when I put my answer in dr frost it's wrong? Maybe it's because I times it by 100 and put it in? I don't know what I did wrong
https://en.m.wikipedia.org/wiki/68%E...80%9399.7_rule
They're well known percemtages. What did you actually enter and what was the solutipn?
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#4
(Original post by mqb2766)
https://en.m.wikipedia.org/wiki/68%E...80%9399.7_rule
They're well known percemtages. What did you actually enter and what was the solutipn?
I put in my answer as 68.2 maybe that's why I got it wrong. I thought I had to times it by 100. I don't know what the actual solution is yet
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1 year ago
#5
(Original post by GogetaORvegito?)
I put in my answer as 68.2 maybe that's why I got it wrong. I thought I had to times it by 100. I don't know what the actual solution is yet
Does the question specify a certain number of significant figures/decimal places?
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1 year ago
#6
(Original post by GogetaORvegito?)
I put in my answer as 68.2 maybe that's why I got it wrong. I thought I had to times it by 100. I don't know what the actual solution is yet
Try 68?
You're basically right.
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#7
(Original post by Interea)
Does the question specify a certain number of significant figures/decimal places?

This is all it says
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#8
(Original post by mqb2766)
Try 68?
You're basically right.
That's it! It was 68! Thanks!
1
1 year ago
#9
(Original post by GogetaORvegito?)
That's it! It was 68! Thanks!
Percentage sometimes means just the integer, but not necessarily always.
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#10
(Original post by mqb2766)
Percentage sometimes means just the integer, but not necessarily always.
Hey could you help me with another one while you're here?
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1 year ago
#11
(Original post by GogetaORvegito?)
Hey could you help me with another one while you're here?
Sure
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#12
(Original post by mqb2766)
Sure
Q: A speed camera is set up on a stretch of road where the speed limit is 50mph.

The speeds of vehicles passing the camera can be modelled by a normal distribution with a mean of 49mph and a standard deviation of 3.5mph.

What speed are the slowest 15% of vehicles travelling below?
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1 year ago
#13
(Original post by GogetaORvegito?)
Q: A speed camera is set up on a stretch of road where the speed limit is 50mph.

The speeds of vehicles passing the camera can be modelled by a normal distribution with a mean of 49mph and a standard deviation of 3.5mph.

What speed are the slowest 15% of vehicles travelling below?
So what do you think?
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#14
(Original post by mqb2766)
So what do you think?
So I did
upper: 15
lower = -10
standard deviation = 3.5
mean = 49
I don't think this is right because I can't get the power sign.
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1 year ago
#15
(Original post by GogetaORvegito?)
So I did
upper: 15
lower = -10
standard deviation = 3.5
mean = 49
I don't think this is right because I can't get the power sign.
I've no idea what you're thinking?

First off, this is similar to the previous question- why?
Then what is the maths expression we want?
Then what are the magic numbers to stick into the calc?
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#16
(Original post by mqb2766)
I've no idea what you're thinking?

First off, this is similar to the previous question- why?
Then what is the maths expression we want?
Then what are the magic numbers to stick into the calc?
Oh is the expression actually X∼N(50<X<15) Then do 1 takeaway that?
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1 year ago
#17
(Original post by GogetaORvegito?)
Oh is the expression actually X∼N(50<X<15) Then do 1 takeaway that?
No. I still don't know what you're thinking. How is it similar to the previous question?
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#18
(Original post by mqb2766)
No. I still don't know what you're thinking. How is it similar to the previous question?
Is it that I have to find two values for z? I'm not sure
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1 year ago
#19
45.3mph (I think - it's 1 am here lol), use the inverse normal function to find the X value when the area is 0.15 1
#20
(Original post by lilyryder)
45.3mph (I think - it's 1 am here lol), use the inverse normal function to find the X value when the area is 0.15 Oh wow we didn't even learn inverse normal function yet. I think this question was an accident if it is. I'll try this anyway thanks
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