The mean of 20 observations is 12.5. By error, one observation was noted as (-15) instead of 15. Then the correct mean is ___?

The correct mean is -12.5.

Step by step explanation:

If one of the 20 observations is a negative number, then the mean would be negative. This is because, when a negative number is in contact with (meaning added, subtracted, multiplied by) a positive number, the whole answer is negative, because it's opposite signs.

Hope this helps! :D

twenty-six miles over two gallons because the proportion for the original 13 miles to one gallon would be written 13/1 and, doing the same thing to the top and bottom, i multiplied by 2 and got 26/2