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Every unique pair of

Fortunately, all normal distributions can be converted into a single distribution, the standardized normal distribution or the *z* distribution, which has mean 0 and standard deviation 1. We write Z ∼ N(0, 1).

The conversion formula for any *x* value of a given normal distribution is:

A *z*-score is the number of standard deviations that a value, *x*, is above or below the mean.

If the value of *x* is less than the mean, the *z* score is negative.

If the value of *x* is more than the mean, the *z* score is positive.

If the value of *x* equals the mean, the *z* score is zero.

This formula allows conversion of the distance of any *x* value form its mean into standard deviation units. A standard *z* score table can then be used to find probabilities for any normal distribution problem that has been converted to *z* scores.

This video shows how to calculate "inside areas" and "areas in the extreme" in a normal distribution using Z-scores.

What is the z-score if our standard deviation was 2, mean of 49 and our specific observation is 47?

What is the probability an observation is more than 49?

What is the probability an observation is more than 47 and less than 49?

What is the probability an observation is more than 47?

What is the probability an observation is less than 47?

You can use the Mathway widget below to practice Statistics or other math topics. Try the given examples, or type in your own problem. Then click "Answer" to check your answer.