Question

Using the statistics table, find the probability of a score less than z = +.88. Write out your answer using all 4 numbers to the left of the decimal.

Answer 1

Z has a standard normal distribution.

The probability of a score less than z=+0.88 is same as the area under the normal curve to the left of z=+0.88, A standard normal curve is drawn with z scores in x-axis and probabilities on the y-axis.

A typical standard normal table lists the probability to the left of the vertical line, but only till z=0. We know that the area under the curve to the left of z=0 is 0.5. the total area under the curve is 1.

We need to find the area under the curve to the left of z=+0.88. In the table we look at the row corresponding to 0.8 and the column corresponding to 0.08 and get a value of 0.3106. But this value is the area under the curve to the left of z=0.088, but only till z=0. Since the area to the left of z=0 is 0.5, we add 0.5 to 0.3106 to get the total area under the curve to the left of z=+0.88. That is 0.5+0.3106=0.8106

ans: The  probability of a score less than z = +.88 is P(Z<0.88) =0.8106