# Anyone good with statistics ? help needed Watch

1. Hi,

Can someone confirm i have done the right thing and just check my answer ?

My question was what percentage of animals should be between 15cm and 20.5cm in length? (normal distribution) using cummulative normal probability table

mean = 18cm sd= 2cm

using the formula i calculated the z value of 15cm to be -1.5 and z value of 20.5cm to be 1.25. Then I looked up in the table to find the p values, which are :

z=-1.5 (p 0.06681)
z=1.25 (p 0.89435)

and then my conclusion: 0.06% of animals should be between 15cm and 0.89% of animals should be between 20.5.

Now i m not sure if this is correct or not, anyone done statistics here ? please look at this and let me know as i dont want to do the wrong thing in my test
2. (Original post by Gamewizard)
Hi,

Can someone confirm i have done the right thing and just check my answer ?

My question was what percentage of animals should be between 15cm and 20.5cm in length? (normal distribution) using cummulative normal probability table

mean = 18cm sd= 2cm

using the formula i calculated the z value of 15cm to be -1.5 and z value of 20.5cm to be 1.25. Then I looked up in the table to find the p values, which are :

z=-1.5 (p 0.06681)
z=1.25 (p 0.89435)

and then my conclusion: 0.06% of animals should be between 15cm and 0.89% of animals should be between 20.5.

Now i m not sure if this is correct or not, anyone done statistics here ? please look at this and let me know as i dont want to do the wrong thing in my test
Is it possible that you could post the full question and mention what exam this is. You may find more help available on the maths forum
3. (Original post by Gamewizard)
My question was what percentage of animals should be between 15cm and 20.5cm in length? (normal distribution) using cummulative normal probability table

mean = 18cm sd= 2cm

using the formula i calculated the z value of 15cm to be -1.5 and z value of 20.5cm to be 1.25. Then I looked up in the table to find the p values, which are :

z=-1.5 (p 0.06681)
z=1.25 (p 0.89435)

and then my conclusion: 0.06% of animals should be between 15cm and 0.89% of animals should be between 20.5.
Well your conclusion makes no sense. You mean zero and 15, and zero and 20.5, right? If this is the case, you can easily work out how many should be between 20.5 and 15 (if you can't, try drawing a diagram).
4. (Original post by Gamewizard)
Hi,

Can someone confirm i have done the right thing and just check my answer ?

My question was what percentage of animals should be between 15cm and 20.5cm in length? (normal distribution) using cummulative normal probability table

mean = 18cm sd= 2cm

using the formula i calculated the z value of 15cm to be -1.5 and z value of 20.5cm to be 1.25. Then I looked up in the table to find the p values, which are :

z=-1.5 (p 0.06681)
z=1.25 (p 0.89435)

and then my conclusion: 0.06% of animals should be between 15cm and 0.89% of animals should be between 20.5.

Now i m not sure if this is correct or not, anyone done statistics here ? please look at this and let me know as i dont want to do the wrong thing in my test
This is very hard to understand without the full details, but those numbers make absolutely no sense whatsoever - '0.89% of animals should be between 20.5', what does that even mean?
Is it possible that you could post the full question and mention what exam this is. You may find more help available on the maths forum
Yeah I have posted this in the maths forum as well. This is one of my normal distribution questions
6. The probabilities from the tables are the area to the left of the z value, so subtract them to get the area between the z values.

They are probabilities, not percentages, so 0.89435 is 89.435%

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