- Let's to speak you'rein the babysitting business and you prefer to save a logof whom you space babysitting. Therefore in the last monthyou babysat six children and also you wrote the periods ofall six kids in her log. Yet then as soon as you go backto her log you notification that some blue ink spilledover one of the ages and you forgot just how old that son is. And at first you're yes, really worried, your whole system ofkeeping documents seems to... You know, you've lost information. However then you remember that every time you composed down a new age that month, you recalculated the mean. And so you have actually themean below of being four, the mean period is four for the six children. So provided that, giventhat you recognize the mean, and also that you recognize fiveout of six of the ages, deserve to you figure out what the sixth age is? and I encourage friend to stop the video and shot to number it the end on her own. Therefore assuming you've had actually a shot at it. For this reason let's just call this missing age, let's speak to that question mark. For this reason let's simply think abouthow execute we calculate, just how would us calculate a typical if we knew what question note is? Well, we would certainly take the total. We would certainly take the complete of ages, that ages, we would then divide that by the number of children. Us then divide that through the variety of ages that us had, and then that would certainly be same to, that would certainly be equal to the mean. Or another method to think about it, if you multiply both sidestimes the number of ages, the variety of ages on the side and also the number of ages on the side, then this is gonna cancel through that, and we're gonna be left with the complete The full is going to be same to, is going to be equal to the average times the number of ages. Mean times, and I'll justwrite time the number, times number of data points, or number of ages. So maybe we deserve to use this information, 'cause we're simply going to have this lacking question note here and we recognize the mean and also weknow the number of ages. So us just have to solvefor the concern mark. For this reason let's execute that. Therefore let's go ago to the start here, simply so this makessense with some numbers. The total of ages, that's going to be five plus two plus concern mark, plus concern mark, add to two, this two, plus two plus 4 plus eight. We're gonna division by the number of ages. We're gonna divide itby the variety of ages. Fine we have six eras here. One, two, three, four, five, six. 6 ages. And that's going come be equal to the mean. This is going come be same to the mean. The mean here is four. So let's see, and this is justhow you calculate the mean. Therefore let's view if we can simplify this. So 5 plus two is seven. Permit me do this, that's the not correct color. Five plus two, 5 plus 2 is seven. Two plus four is six plus eight is 14. 14. And then 7 plus 14 is 21. Therefore we're left through 21 to add question mark over 6 is equal to four. Now we can do what we didwhen we simply wrote it every out. We deserve to multiply both sidestimes the number of ages, the number of data points we have. For this reason we have the right to multiply both political parties times six. We can multiply both sides, both political parties times six. So 6 on that side, six on this side. Six in the numerator, six inthe denominator, those cancel. So all we're left is, ~ above the left-hand side we'releft v 21 plus concern mark. Alright. All of these other eco-friendly numbers, those just simplified, five plus two plus twoplus 4 plus eight is 21 and also we still have actually the question mark. For this reason we acquire 21 plus inquiry mark, I want to perform that eco-friendly color, 21 add to this inquiry mark, the point that we're do the efforts to resolve for. The missing number isgoing come be same to, is going to be same to four times six. Fine what's four times six? That's 24. And so what's the inquiry mark? 21 add to what is equal to 24? and we could, the course, you could just say, wellit's gonna be three. Or, if you desire to, you might say well, question mark is going come be, question mark is going to be same to, is going come be equal to 24 minus 21. I beg your pardon is, the course, three. I m sorry of course, therefore letme simply write this down, for this reason the question mark is same to three. So the lacking age, youwere may be to number it out based on the details you had, due to the fact that you had actually the mean, you to be able to figure outthat behind this blotch, that behind this blotch you had a three. It's exciting.

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Mean as the balancing point
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Mean as the balancing point
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