Thread: [SOLVED] Normal approximation to binomial

I've tried so many things but I never get the correct answer. Here's an example:

For Find using a normal approximation

This is what I do:




But at this point, I get in a mess.

The correct answer is 0.9596

Thanks in advance for any replies.

Originally Posted by Quacky

I've tried so many things but I never get the correct answer. Here's an example:

For Find using a normal approximation

This is what I do:




But at this point, I get in a mess.

The correct answer is 0.9596

Thanks in advance for any replies.

Remember


Now employ

So

Can you contiune?

Thanks for the fast reply, but seemingly not










Which is incorrect. Am I using the tables incorrectly? Or is there something wrong with my method?

I would say

0.9596 is the correct answer though, so I'm confused.

All I can suggest is to use a better approximation for . Otherwise the methodology seems good to me.

I suggest you apply a "correction for continuity", so instead of finding
P(3 < Y < 13),
you find
P(2.5 < Y < 13.5),
where Y has a Normal distribution with mean 8 and standard deviation 2.19.
This leads to
P(-2.51 < Z < 2.51)
where Z has a Normal(0,1) distribution, yielding a probability of 0.988.

(Yes, I know, that's not the answer in the book. Sometimes the book has the wrong answer.)

Hm. Seeing as we're all getting around that, I suppose it must be right. Thanks again.