Using Bar Models To Solve Percentage Problems

Hi, I'm Luke, and today we're going to be using a bar model to solve a word problem involving percentages. So let's have a look at the question. Out of a school of 240 wizards and witches, 70% had a pet owl. The remaining wizards and witches had a pet toad. How many had a pet toad? So, as we've done before, we can use a bar model to represent our whole. Now, in this case, our hole is 240 Wizards and Witches. So we can represent this here. This is our whole of wizards and witches. And as that is our whole, our total, we can also represent this as 100%. Now, we already know that 70% had a pet owl, so we should also show this on the bar model. So it's clear to the pitbills. Now, the remaining wizards and witches had a pet toad, so this is the remaining bit. We've got a hundred percent of total. We've already got 70%, so we need to work out 100 minus 70, and that gives us 30. So this remaining bit here is 30%. Now, when you're using bar models to do with percentages, it's often very helpful to have another bar model that is split into tens. So each section here represents 10. 10%. Now, in order to work out what the answer is for 10%, we need to do 240 divided by 10. You can get a pupil up to the board to answer this out if you wish. The answer is 24. So each part here is worth 24. Now, at this point, it is important to refer back to the question, because we've done lots of different working outs, but we haven't actually got to the crux of the problem here. So we know that we've got our 70%, and we're trying to work out how many had a pet toad. We've got our remainder of 30%, so we're trying to work out this section here. Now we know what 10% is. 10% is 24, and we need to times that by three, because we're trying to work out three lots of 10%, and that's going to give us 72. And now we're able to answer the question. We have 72 tones, and that's how you work out a question involving percentages, using a bar model.