Calculator Error - Normal Distribution
When I type in certain numbers in Normal CD on my fx-991EX calculator, it seems to give me a different answer to what I should get.
For example, P(X<30) with X~N( 32.5 , 2.2^2 )
I type in
Lower=-999
Upper=30
Standard Deviation=2.2
Mean=32.5
I get 0.872098... however it says that I should be getting 0.12790..
Am I doing something wrong or is my calculator wrong?
For example, P(X<30) with X~N( 32.5 , 2.2^2 )
I type in
Lower=-999
Upper=30
Standard Deviation=2.2
Mean=32.5
I get 0.872098... however it says that I should be getting 0.12790..
Am I doing something wrong or is my calculator wrong?
Original post by depriveofsocial
When I type in certain numbers in Normal CD on my fx-991EX calculator, it seems to give me a different answer to what I should get.
For example, P(X<30) with X~N( 32.5 , 2.2^2 )
I type in
Lower=-999
Upper=30
Standard Deviation=2.2
Mean=32.5
I get 0.872098... however it says that I should be getting 0.12790..
Am I doing something wrong or is my calculator wrong?
For example, P(X<30) with X~N( 32.5 , 2.2^2 )
I type in
Lower=-999
Upper=30
Standard Deviation=2.2
Mean=32.5
I get 0.872098... however it says that I should be getting 0.12790..
Am I doing something wrong or is my calculator wrong?
Try making the lower ~10?
(edited 8 months ago)
Original post by depriveofsocial
When I type in certain numbers in Normal CD on my fx-991EX calculator, it seems to give me a different answer to what I should get.
For example, P(X<30) with X~N( 32.5 , 2.2^2 )
I type in
Lower=-999
Upper=30
Standard Deviation=2.2
Mean=32.5
I get 0.872098... however it says that I should be getting 0.12790..
Am I doing something wrong or is my calculator wrong?
For example, P(X<30) with X~N( 32.5 , 2.2^2 )
I type in
Lower=-999
Upper=30
Standard Deviation=2.2
Mean=32.5
I get 0.872098... however it says that I should be getting 0.12790..
Am I doing something wrong or is my calculator wrong?
Typing those same numbers into my calculator(same model) gives me 0.127902204
Original post by Skiwi
Typing those same numbers into my calculator(same model) gives me 0.127902204
Looking at the numbers it could be > rather than <.
Original post by mqb2766
Looking at the numbers it could be > rather than <.
That crossed my mind as what had happened(after calculating the other value manually via asymptotic expansions instead of just spotting they added to 1 i must admit), but the casio automatically calculates < which is what the textbook is suggesting is the correct answer. Unsure as to how OP has got what they've got, unless there's a setting that lets you swap the sign the calculator solves that I'm unaware of. OP try resetting your calculator with shift - 9 -3 - = - AC.
Original post by mqb2766
Looking at the numbers it could be > rather than <.
I wonder why tho
Original post by Skiwi
That crossed my mind as what had happened(after calculating the other value manually via asymptotic expansions instead of just spotting they added to 1 i must admit), but the casio automatically calculates < which is what the textbook is suggesting is the correct answer. Unsure as to how OP has got what they've got, unless there's a setting that lets you swap the sign the calculator solves that I'm unaware of. OP try resetting your calculator with shift - 9 -3 - = - AC.
I tried the shift, it didn’t change what I got, i think its the values
Original post by mqb2766
Try making the lower ~10?
Yes, i got 0.1279.. when the lower was 10, do you know why that was?
Original post by depriveofsocial
Yes, i got 0.1279.. when the lower was 10, do you know why that was?
Its surprising that the original value was 1-#, but from memory, the calc uses an approximate/numericall algorithm for finding the area under the curve so when you put in lower=-999 you have a curve like
https://www.desmos.com/calculator/m6bzmagnk2
to integrate (to see the interesting bit of the normal distribution, look in the very bottom right and note Ive not but the 1/2... scaling in but thats hardly relevant). Its "hard" as its "zero" almost everywhere.
Changing the lower limit to 10 would make the curve easier to numerically integrate (click on the spanner and change the min x value to viualise it). The lower limit only needs to be about about 10 standard deviations lower than the mean so lower=10 in this case would be sufficient and give your calc (numerical algorithm) a chance. Its not that sensitive but lower probably wants to be more than 5 standard deviations less than the mean and not be horrendously large.
However, the original value of 1-# is weird, in the past the calc returned "random" values for this problem. So this may not be the reason.
(edited 8 months ago)
Check the sign!
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