# Video: Finding the Number of Observations in a Set of Data

The tally chart shows the number of hours different students spent studying over a week. How many hours did Noah spend studying?

02:21

### Video Transcript

This tally chart shows the number of hours different students spent studying over a week. How many hours did Noah spend studying?

The tally chart shows the names of four different students: Noah, Madison, Daniel and James. The second column of our tally chart shows the number of hours that each student spent studying over the course of a week. But instead of showing the number of hours written as a number, it’s written as a series of tally marks.

Let’s remind ourselves some facts about tally marks. Firstly, each line stands for one, and that’s why they’re a quick way of recording something. It’s very quick to do this and to draw lines to represent one each time. When we get to a set of five tally marks, we draw the fifth mark across the four. This makes a set of five, and it helps us to count the tally marks quickly. This question is all about reading and interpreting the tally chart that we’ve been given.

We’re asked, how many hours did Noah spend studying? So, we don’t need to look at any of the other students. We just need to concentrate on the top row, which tells us the hours that Noah spent studying. To count the tally marks correctly, we need to skip count in fives for each set of five tally marks that we can see. Five, 10, 15, 20, 25. There are five sets of five which equals 25. But, we can also see two more tally marks on the end. 25 plus two equals 27.

To find the number of hours that Noah spent studying in a week, we counted in fives for each set of five tally marks that we could see. We’ve encountered the two ones on the end. Five, 10, 15, 20, 25, 26, 27. Noah spent 27 hours studying.