Stats help
The length of a particular component is normally distributed with a mean of 100cm and and standard deviation of 8cm, what is the probability of the component having a length of more that 82cm?
Could anyone please give step by step answer to that question?
Posted from TSR Mobile
Could anyone please give step by step answer to that question?
Posted from TSR Mobile
Original post by Blyts-_
The length of a particular component is normally distributed with a mean of 100cm and and standard deviation of 8cm, what is the probability of the component having a length of more that 82cm?
Could anyone please give step by step answer to that question?
Posted from TSR Mobile
Could anyone please give step by step answer to that question?
Posted from TSR Mobile
Do you know how to convert that '82' into a Z value?
Original post by SeanFM
Do you know how to convert that '82' into a Z value?
I don't think so, I'm new to stats you see. What I did was (82-100)/8= -2.25 and then looking at the tables, I got 0.9878 as my final answer, is this correct
Posted from TSR Mobile
Original post by Blyts-_
I don't think so, I'm new to stats you see. What I did was (82-100)/8= -2.25 and then looking at the tables, I got 0.9878 as my final answer, is this correct
Posted from TSR Mobile
Posted from TSR Mobile
That's good, you know how to get to z values
The thing about it is that the table uses P(Z ≤ z).
In the question you're looking for P(length>82), and you've converted it to P( Z > -2.25 ). But the table gives values for P(Z ≤ z). You've correctly read off 0.9878 (I think) for P (Z < +2.25) , but you need to change that into P(Z > -2.25).
Have you learned how to go from P(Z ≤ z) to P(Z > z) and how to deal with negative numbers with z?
Original post by SeanFM
That's good, you know how to get to z values
The thing about it is that the table uses P(Z ≤ z).
In the question you're looking for P(length>82), and you've converted it to P( Z > -2.25 ). But the table gives values for P(Z ≤ z). You've correctly read off 0.9878 (I think) for P (Z < +2.25) , but you need to change that into P(Z > -2.25).
Have you learned how to go from P(Z ≤ z) to P(Z > z) and how to deal with negative numbers with z?
The thing about it is that the table uses P(Z ≤ z).
In the question you're looking for P(length>82), and you've converted it to P( Z > -2.25 ). But the table gives values for P(Z ≤ z). You've correctly read off 0.9878 (I think) for P (Z < +2.25) , but you need to change that into P(Z > -2.25).
Have you learned how to go from P(Z ≤ z) to P(Z > z) and how to deal with negative numbers with z?
No I'm afraid I haven't learn that yet. Any chance you could briefly explain it?
Original post by Blyts-_
No I'm afraid I haven't learn that yet. Any chance you could briefly explain it?
Hmm, not sure why you've been asked that then. It's best to go and look it up but:
P( Z ≤ z) = 1 - P( Z > z). Can you see why that would make sense?
And when you're dealing with a negative number, -z , where z is a positive number,
P ( Z ≤ -z) = 1 - P ( Z ≤ z). This is due to the symmetry of the normal distribution.
But as I said, best to look at your textbook or ask your teacher about it.
And also in these types of questions it's best to 'convert' your working into something in terms of P ( Z ≤ z) before referring to the massive table, but this is something you'll pick up soon enough.
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