[The narrator reads out the onscreen text.]

NARRATOR: Question one. In a class, there are 9 girls and 16 boys. What percentage of the class are: a - boys, b - girls? Part a. What percentage of the class are boys? There are 16 boys out of a total of 25 students in the class, so the fraction of the class that is boys is 16 out of 25. To convert this fraction to a percentage, we multiply by 100%. 16 over 25 multiplied by 100 over 1 per cent. We can cancel these fractions down because 25 goes into 100 four times so we have 16 multiplied by 4%, which gives 64%. So 64% of the class are boys.

Part b. What percentage of the class are girls? Given that we know 64% of the class is boys, that means 100% - which is the entire class - minus the 64% - which is the proportion of the class that are boys - leaves 36% of the class which must be girls.

Alternatively, we could have used the same method we used in Part a, and noted that we had 9 out of 25 in the class were girls, multiplied by 100% to convert to a percentage, which also would have given 36%.