Hi, I'm Steve Jones and I'm going to look at calculating a weighted average. Now, a weighted average is not really different from an average. It's just a different way of looking at averages, and obviously, if I gave you a list of numbers, like six, five, four, three, I could work out the average. So the average of these numbers is six plus five plus four plus three....eighteen...and there are four numbers, so it's eighteen divided by four. Now, eighteen divided by four, is, of course, 4.5. Right? So the average of those four numbers is 4.5. But, what this doesn't say is what happens when you have, for example, not one of these numbers, but maybe more than one of the numbers. So let's say you've got a list of numbers of this kind. Now, obviously, I can't say six plus five plus four plus three, and divided by...the...overall number. The weighted average, although the numbers six, five, and four and three are the only numbers in the sequence, six is more important and three is more important in this case. So we have to make allowances. So the weighted average of these, which is the same as the average, is eighteen plus nine, which is twenty seven, thirty six, in this case. But divided by three, six, eight. And, we've got, therefore, twice the number of numbers, but there are more threes and more sixes, and just one each of five and four. Okay, so four eights are thirty two. The weighted average in this case turns out to be also 4.5. Now, you might say, "Well, what's the difference?" The big difference would be if, instead of the number three being there, we had six, six and six, and then five and four and three, without the extra threes, we would then have thirty, this time divided by six, which gives us an average of five. So the weighted average takes in to the....takes into account the number of objects, or how strong that value is represented in the set of numbers that you've got. So you have to take account of how many times it occurs.