Hi, I'm Peter Edwards from Bluetutors. We teach children of all ages, right from primary school to degree level, and we find the highest quality tutors. Today, I'm going to teach you some maths. Okay, so now we're going to look at how to calculate percentile. What this generally refers to is the scores on peoples' exams, say where someone says “I was in the ninety-ninth percentile” and we want to work out what that means. All percentile is, is a way of saying of grouping the scores. So if you have an ordered number of scores, you can say the twenty-fifth percentiles are those scores which are lower than twenty-five percent of the way through those scores. So if you look at an example on this graph, we have test score along the bottom axis, and the frequency of people below that test score on the y-axis. So as you can see, one hundred percent of the people are going to be one hundred percent of the test score, because you can only get up to one hundred percent. So we'll look at three main percentiles that are dealt with a lot. If you look, we've already mentioned the twenty-fifth percentile which is also called the first quartile. That will just refer to the number of people who are in the bottom twenty five percent of that test score. If you look at that, we can go across the graph and see that that is forty-five percent on the test. Similarly, we have quartile two, which is fifty percent, and fifty percent of the people scored fifty-five or lower on this test. Q two is also often referred to as the median. We have Q three which is seventy-five percent, so this is the third quartile. If we look on the graph, we can see that seventy-five percent of the people scored seventy of lower on a test. It's a bit of a strange one, because if you were to say that you were in the seventy-fifth percentile, people normally take that to mean above seventy-five percent of the rest of the class. In fact, it doesn't actually mean that, it means below but it's been used to mean, a lot of the times, that you're above it. It's a way of saying how good you were on a particular test. So, for example, we could look at the ninety-ninth percentile, which would be up here and that might be, say, ninety-two on the test. So, if you scored ninety two or above on the test, you would be above the ninety-ninth percentile. That's what percentile is, and how to work one out. .

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