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 Post subject: Average (Mean)Posted: Sun Mar 16, 2014 10:22 pm

Joined: Mon Aug 12, 2013 9:13 am
Posts: 452
Just wondering what's the recommended (quick & accurate) way to add the following 10 numbers for finding mean.

46, 47, 43, 46, 45, 49, 45, 43, 45, 41

2. Pairing where possible 49+41 = 90, 45 + 45 = 90. And then add the remainder numbers
3. 40 x 10 = 400 + add all units

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 Post subject: Re: Average (Mean)Posted: Sun Mar 16, 2014 10:33 pm

Joined: Fri Mar 07, 2014 6:50 am
Posts: 69
Hi, I would defiantly choose method 3....40 x 10=400 then add the rest!

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 Post subject: Re: Average (Mean)Posted: Sun Mar 16, 2014 10:50 pm

Joined: Tue Dec 18, 2012 10:59 am
Posts: 3579
Deffo number three then number bond the units where possible.

Your ds has done it a barmey way I presume, and told you his teacher said he had to!

Tbh how often would you get 10 numbers (easy to multiply) and all numbers had the same amount of tens?

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 Post subject: Re: Average (Mean)Posted: Mon Mar 17, 2014 5:23 am

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8228
As you can see it is going to be 40 something why not just add the digits in the units column and find the mean of those. The units look as though they have been chosen for easy pairing into pairs of numbers which add to 10 for a primary child - I find adding in order faster than doing this pairing though --- should be really for any child higher up primary.

Yes, clearly not real data!

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 Post subject: Re: Average (Mean)Posted: Mon Mar 17, 2014 8:15 am

Joined: Sat Aug 10, 2013 11:46 am
Posts: 188
I agree with Mystery, find the average of the digits, then add on 40.

There is a similar question which often comes up about finding a missing number if you are given the mean. So say you were given the mean of 45, but not the last number of 41. The text book way to find the number is to add all the numbers then subtract this from 45*10.

The tip I gave dd was to go through the numbers giving them a value of how much less or more they are from 45. So for the list given the numbers you would get are
1,2,-2 ,1,0,4,0,-2,0.
This adds up to 4. So the missing number must be 4 less than 45.

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 Post subject: Re: Average (Mean)Posted: Mon Mar 17, 2014 4:11 pm

Joined: Mon Aug 12, 2013 9:13 am
Posts: 452
Most of the time I see pairs of number that can be easily added together to speed up totals but saw this Q where pairing doesn't really work and thought to check. All very good replies.

Thanks.

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