You would have to add up the total participants in the survey first. So, 30+35+40+25+10=140. Now, you would take the number of people under 17 (30) and divide it by the total participants (140). 30/140=21.4%. Hope this helps.
Ok, so when you're reading the bar graph, you can tell how many participants are in each group by looking at the y-axis. For example, there are 30 people under 17. There are 35 people aged 18-24, etc. The numbers on the y-axis you add up. So 30 (for under 17)+35(for 18-24), etc. Now, a percentage is basically a proportion. So the whole, which in this case is the total amount of people surveyed, will always be the denominator. Then the portion that we are trying to find, which in this case is the people surveyed under 17, will be the numerator. Hence, 30/140.
