Let's try subtracting now. How do we solve 5 - (-3)? Tip: Subtracting a negative is the same as adding a positive. So 5 - (-3) is the same as 5 + 3.Another way of thinking of it, is two minuses make a positive.
To add a negative number, you subtract its positive equivalent. 3 + -3 is 3 - 3, which is 0. to subtract a negative, you add. 3 - -3 is 3 + 3, which is 6.
Problems of normally distributed samples are solved using the z-score formula.
In a set with mean and standard deviation , the zscore of a measure X is given by:
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.