Answer if different from book :/ (Binomial approximation)

Hi there.

I've attached the question and my working out but it is different to the book's answer of 0.4540 (I think this is also rounded).

There is no working out in the book. They only give the end answer.

Can someone spot where I have gone wrong as I can't see it.

Thanks

Reply 1

username1732133

Original post by jojo55

It's your last step.

P(a<x<b) = P(x<b) - P(x<a)

Edit: You can check your answer here: https://burymathstutor.co.uk/normal.html

(edited 3 years ago)

Reply 2

jojo55

Original post by Plücker

It's your last step.

P(a<x<b) = P(x<b) - P(x<a)

Edit: You can check your answer here: https://burymathstutor.co.uk/normal.html

Thanks for the quick reply. I can see where I have gone wrong now.

I've still got a different answer to the book's answer of 0.4540.

I've used your link and got the same answer as when I worked it out again.

Screen Shot 2020-07-01 at 10.08.35.png

. Is the book's answer incorrect?

Screen Shot 2020-07-01 at 10.08.35.png36.3KB

Screen Shot 2020-07-01 at 10.10.05.png142.8KB

Reply 3

ghostwalker

Original post by jojo55

Is the book's answer incorrect?

55.5

Where did that come from? Have another go.

Reply 4

jojo55

Original post by ghostwalker

55.5

Where did that come from? Have another go.

Whoops. Corrected it now but still am not at the book's answer of 0.4540 :s-smilie:

Screen Shot 2020-07-02 at 14.59.16.png131.8KB

Reply 5

old_engineer

Original post by jojo55

Whoops. Corrected it now but still am not at the book's answer of 0.4540 :s-smilie:

Not quite. The range of values (60 < X =< 72) means the set {61, 62, 63 .... 70, 71, 72}. So the values you need to exclude are {0, 1, 2 ... 58, 59, 60}. Your current working fails to exclude X = 60.