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S1 Normal Distribution question

Hey everyone.

I'm in need of some help with a particular stats question:

The weights of letters posted by a certain business are normally distributed with mean 20 g. It isfound that the weights of 94% of the letters are within 12 g of the mean.
(i) Find the standard deviation of the weights of the letters.

Any help will be much appreciated :smile:

Reply 1

Kevin De Bruyne

Original post by Inferno_salmai

Hello

If it is given that 94% of the letters are within 12g of the mean, can you set up an inequality to show that?

Another method may be to sketch the normal distribution curve, label the mean and the two points where between them 94% of the letters are and see if you can think what to do, observing what % of letters aren't within 12g of the mean on the other sides of the two points.