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Help , can't read this normal distribution table

image.jpgWhen the probability is 0.8 what is z? It says on a markscheme it is 0.842??? How???
Find the value in the table that is closest to 0.8. In this case, it's 0.7995 and it's towards the top left of the table. Trace it to the left to get the first digit, the 8 and up to get the second digit, the 4. So far we're at a z-score of .084 0.8 is 0.005 off from the 0.7995 on the table though, so trace the column all the way to those single and double digits at the right and find the one closest to 5, in this case a six. Trace it up and it lines up with the last digit, a 2.

For practice, try to find the z-score of something with a probability of 0.8628. Can you see how it's 1.093? What about P=0.8355 with z=0.976?

As a side note, if I hadn't been able to load this picture on my ipad and physically rotate it, I wouldn't have helped. Tables on a computer screen are rough enough to read; orientating them the right way is probably a good way to increase the odds of people taking the time to help you.
Reply 2
ImageUploadedByStudent Room1401106356.363770.jpg This table gives P(Z>z) so look for >0.2 which is 0.8416


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Reply 3
Original post by ktalexander
Find the value in the table that is closest to 0.8. In this case, it's 0.7995 and it's towards the top left of the table. Trace it to the left to get the first digit, the 8 and up to get the second digit, the 4. So far we're at a z-score of .084 0.8 is 0.005 off from the 0.7995 on the table though, so trace the column all the way to those single and double digits at the right and find the one closest to 5, in this case a six. Trace it up and it lines up with the last digit, a 2.

For practice, try to find the z-score of something with a probability of 0.8628. Can you see how it's 1.093? What about P=0.8355 with z=0.976?

As a side note, if I hadn't been able to load this picture on my ipad and physically rotate it, I wouldn't have helped. Tables on a computer screen are rough enough to read; orientating them the right way is probably a good way to increase the odds of people taking the time to help you.

thanks so much for helping despite the orientation of the picture i uploaded being an awkward way! i can't see how the z value of 0.8628 is 1.093? i went to 0.8621 on the table (closest to 0.8628) then across to 1.1 and up to 0.09.. the the closest value to 1 (the last digit of 0.8621) is 2. so 1.1092? this is wrong, i know :frown: what have i did wrong
Reply 4
Original post by Mr Tall
thanks so much for helping despite the orientation of the picture i uploaded being an awkward way! i can't see how the z value of 0.8628 is 1.093? i went to 0.8621 on the table (closest to 0.8628) then across to 1.1 and up to 0.09.. the the closest value to 1 (the last digit of 0.8621) is 2. so 1.1092? this is wrong, i know :frown: what have i did wrong


See post three from jm4425.
Original post by Mr Tall
thanks so much for helping despite the orientation of the picture i uploaded being an awkward way! i can't see how the z value of 0.8628 is 1.093? i went to 0.8621 on the table (closest to 0.8628) then across to 1.1 and up to 0.09.. the the closest value to 1 (the last digit of 0.8621) is 2. so 1.1092? this is wrong, i know :frown: what have i did wrong


0.8628=0.8621+.0007. You've got the first two steps correct, but you still need to add on that last .0007. Use the columns on the far right; there are three of them and they're titled "(ADD)". Trace over to the 7 and then up to the 3, which gives you the final digit for your z-score.

These tables are a little bit tricky to get the hang of at first, but once you've got it, they aren't bad at all. You can generate your own practice problems and check them by using an online inverse norm calculator like this one.
(edited 9 years ago)
Reply 6
Original post by ktalexander
0.8628=0.8621+.0007. You've got the first two steps correct, but you still need to add on that last .0007. Use the columns on the far right; there are three of them and they're titled "(ADD)". Trace over to the 7 and then up to the 3, which gives you the final digit for your z-score.

These tables are a little bit tricky to get the hang of at first, but once you've got it, they aren't bad at all. You can generate your own practice problems and check them by using an online inverse norm calculator like this one.

really sorry but i dont get that? trace over to the 7? there is no 7.. only a 2, 4 and a 6
I just reread what you wrote in post 4. You're in the wrong row. It's the 1.0 row that has 0.8621, the 1.1 row has 0.8830.

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