00:00This video is part of a Google Form quiz that teachers can assign to their students for
00:05homework. After the students submit their answers, then they can play a video like
00:09this one to see the answer explained. We've made more than 100 quizzes as Google Forms
00:15with free access videos, which teachers are welcome to copy for free. To get access to these,
00:21please see the link in the description. This video is based on a question from an
00:26actual state exam. You may have one like this on your state exam. If you've not already watched
00:32the video on how to calculate the average, then we suggest that you view it before watching this
00:37video. The list shows the lengths in minutes of nine speeches. What is the mean length of the speeches?
00:45We define the mean as the answer to a division problem. In everyday language, we use the word
00:50average instead of the word mean. The word mean is used on math tests and in math books,
00:57but has the same idea and formula as the word average. The mean of a set of numbers equals the
01:03sum of those numbers divided by the number count. There are nine numbers in this list, so the number
01:09count for this set is nine. The sum of these items is the total of 28 plus 21 plus 14 plus 33 plus 14
01:19plus 30 plus 28 plus 21 plus 18. That sum equals 207. Here's the formula for the mean. The mean equals
01:30the sum of the numbers divided by the number count. We substitute the phrase sum of numbers with 207.
01:37We substitute the phrase number count with 9. Then we do the division. 207 divided by 9 equals 23.
01:45The mean for this group is 23. The mean length of these speeches is 23 minutes. Choice C is correct.
01:52Thanks for your attention.
