posted by Julia Ten on .
the average of 20 numbers in a list is 32. when a number is added to the list, the average becomes 34. What number was added to the list?
so i started like this...
my answer is 640. is this correct?
think backwards, and how "average" is obtained
the average of 20 numbers was 32, so the total of all the numbers must have been 20x32 or 640.
For 21 numbers the average was now 34, so the total must have been 21x34 or 714
so 714-640 or 74 must have been the number added