- Let's speak you'rein the babysitting business and also you prefer to save a logof whom you space babysitting. So in the critical monthyou babysat 6 children and also you wrote the ages ofall six kids in her log. Yet then once you go backto your log you an alert that part blue ink spilledover among the ages and you forgot just how old that child is. And also at an initial you're really worried, your totality system ofkeeping documents seems to... Girlfriend know, you've lost information. However then girlfriend remember the every time you created down a brand-new age that month, you recalculated the mean. And also so you have actually themean here of being four, the mean age is four for the six children. So offered that, giventhat you know the mean, and also that you know fiveout of 6 of the ages, have the right to you number out what the sixth age is? and also I encourage friend to stop the video clip and try to number it the end on your own. Therefore assuming you've had actually a shot at it. Therefore let's just call this absent age, let's call that inquiry mark. Therefore let's just think abouthow execute we calculate, just how would us calculate a median if we knew what question note is? Well, we would take the total. We would certainly take the full of ages, of ages, we would then divide that by the variety of children. Us then divide that by the number of ages that us had, and also then that would be same to, that would be equal to the mean. Or another way to think around it, if you main point both sidestimes the variety of ages, the variety of ages on that side and also the variety of ages on that side, then this is gonna cancel with that, and we're gonna it is in left through the total The total is going come be equal to, is going come be equal to the median times the number of ages. Median times, and I'll justwrite time the number, times variety of data points, or number of ages. So maybe we can use this information, 'cause we're simply going to have actually this lacking question note here and also we know the mean and weknow the variety of ages. So us just have to solvefor the inquiry mark. So let's perform that. For this reason let's go earlier to the start here, just so this makessense with some numbers. The full of ages, that's going to be five plus 2 plus inquiry mark, plus question mark, plus two, this two, plus two plus four plus eight. We're gonna division by the number of ages. We're gonna division itby the variety of ages. Well we have six eras here. One, two, three, four, five, six. 6 ages. And also that's going to be same to the mean. This is going to be same to the mean. The mean right here is four. For this reason let's see, and this is justhow you calculate the mean. So let's watch if we have the right to simplify this. So 5 plus two is seven. Let me carry out this, that's the wrong color. Five plus two, five plus two is seven. Two plus four is 6 plus eight is 14. 14. And also then 7 plus 14 is 21. Therefore we're left v 21 to add question note over 6 is equal to four. Currently we deserve to do what us didwhen we simply wrote it all out. We deserve to multiply both sidestimes the variety of ages, the variety of data points we have. For this reason we deserve to multiply both sides times six. We have the right to multiply both sides, both sides times six. So six on the side, 6 on this side. 6 in the numerator, six inthe denominator, those cancel. So every we're left is, on the left-hand next we'releft v 21 plus concern mark. Alright. Every one of these other eco-friendly numbers, those simply simplified, five plus two plus twoplus four plus eight is 21 and we still have actually the concern mark. So we acquire 21 plus inquiry mark, I want to execute that eco-friendly color, 21 to add this concern mark, the point that we're make the efforts to resolve for. The missing number isgoing come be equal to, is going come be equal to 4 times six. Fine what's four times six? That's 24. And so what's the concern mark? 21 add to what is same to 24? and also we could, of course, you could just say, wellit's gonna it is in three. Or, if you want to, you can say well, question mark is going to be, question note is going come be equal to, is going come be same to 24 minus 21. I m sorry is, of course, three. I m sorry of course, therefore letme just write this down, therefore the question note is same to three. Therefore the missing age, youwere able to figure it out based on the information you had, due to the fact that you had actually the mean, you to be able to number outthat behind this blotch, the behind this blotch you had a three. It's exciting.

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