# Thread: Reading z-tables when you know the probability

1. ## Reading z-tables when you know the probability

I'm having trouble reading z tables.

If anyone can help I'd be thankful as I feel I can't move on until I know how to do this.

One of the examples in my text book states the probability that z is greater than zi is 0.06.

1-0.06 = 0.94. I get everything up to this point.

Next, if we look up 0.94 in the body of the Table A it gives us a z-score of 1.56.

I don't see how you can look this up in the table as the table only goes up to 0.5000. Is my table different?

Can someone tell me where I would get 1.56 from? Thanks in advance

I've watched a few online tutorial videos such as this one: http://www.youtube.com/watch?v=2Xp5y...eature=related on how to read the table and all they say is if you look at the table you will see... Umm not in my case!

Any help would be appreciated.

Many Thanks!

2. ## Re: Reading z-tables when you know the probability

One nice thing about the standard normal distribution is that it's symmetric. What this gives us is that P(Z < 1.56) = 1 - P(Z < -1.56).

Well technically what that gives us is that P(Z > x) = P(Z < -x) but we can use this fact to derive the above fact.

3. ## Re: Reading z-tables when you know the probability

I managed to find a 2-sided table In Moore and McCabe's book 'Introduction to the practice of statistics'.

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