In an experiment, the average of 13 observations is 45, while the average of first six observations was 21, and that of the last six was 27. What was the measure of the 7^th observation?

The total sum of all 13 observations is 13 times 45, which equals 585. The sum of the first six observations is 6 times 21, giving 126, and the sum of the last six is 6 times 27, giving 162. The 7th observation is the total sum minus the sum of these twelve observations, so it is 585 minus 126 minus 162, resulting in 297.

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