Question

The mean of 19 observations is 12. Also the mean of first 10 observations is 13 whereas the mean of last 10 observations is 11. Find the 10th observation.

Answer 1

the mean of 19 observations is 12

the total sum of 19 observations :

19 * 12

228

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mean of first ten observations is 13

total sum of first ten observations :

10 * 13

130

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mean of last ten observations is 11

sum of last ten observations :

10 * 11

110

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total sum of 20 observations is now :

130 + 110

240

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due to first and last ten numbers :

10th observation is repeated

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tenth observation :

sum of 20 observations - sum of 19 observations

240 - 228

12

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$\bold{10 \: th \: observation \: is \: 12}$

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