Question

The mean rate for internet from a sample of householdswas $30 per month, with a standard deviation of $2.50 permonth. The data set has bell-shaped distribution.Estimate the percent of internet rates between $27.50 and$35?

Answer 1

step 1

Find the z-score

For x=$27.50

z=(27.50-30)/2.50

z=-1

For x=35

z=(35-30)/2.50

z=2

using Standard Normal Distribution Tables

between z=0 and z=2 ------> P=0.4772

between z=-1 and z=0 -----> P=0.3413

therefore

P=0.4772+0.3413

P=0.8185

P=81.85%

answer is 81.5%