3.4 Percentiles and Box and Whisker Plots Percentiles For whole numbers P, where P is between 1 and 99 (including 1 and 99) the Pth percentile of a distriubiton means that P% of the data fall AT OR BELOW it and 100-­‐
P % fall AT OR ABOVE it. If you score in the 89th percentile, what percentage of scores are at or below yours? If you take a test and get a 95 out of 100 points, does this mean that your score is at the 95th percentile? Quartiles: the percentiles that divide the data into fourths. 25th Percentile-­‐ 50th Percentile-­‐ 75th percentile-­‐ HOW TO FIND QUARTILES 1. Order the data from smallest to largest 2. Find the median, this is the 2nd quartile 3. The first Quartile Q1, is then the median of the lower half of the data, ONLY FIND THE MIDDLE OF THE DATA BELOW THE MEDIAN (DON’T INCLUDE THE MEDIAN) 4. The third Quartile q3, is the median of the upper half of the data, ONLY FIND THE MIDDLE OF THE DATA ABOVE THE MEDIAN (DON’T INCLUDE THE MEDIAN) Find the median and quartiles of the cost of Ice Cream Bars .16 .17 .18 .20 .25 .33 .33 .35 .37 .50 .50 .50 .63 .84 .97 .97 .99 1.00 1.07 1.08 1.23 Find the median and quartiles of the calories in ice cream bars 111 131 147 151 151 182 182 190 197 286 294 295 310 319 342 353 377 377 .38 .40 .47 1.03 1.07 1.07 201 439 209 234