Question

12 adults reading on the beach were surveyed about the number of total books they read in a typical summer. The mean number of books read was 5.5. A thirteenth adult was surveyed and said she read a whopping 25 books each summer. What is the new mean for the 13 adults?

Answer 1

Answer: 7

Step-by-step explanation

S = sum of the number of books the 12 people have read

S/12 = average number of books those 12 people read

S/12 = 5.5

S = 12*5.5

S = 66

If we add up all of the books the original 12 people have read, then we get 66 books.

Add on the 13th person's book count to get 66+25 = 91 books total. Divide that new sum over the new sample size (13).

91/13 = 7

The new mean is 7.

The old mean 5.5 has increased to 7. This is to be expected because the large outlier pulls on the mean like a gravitational force or a magnet. In fact, all of the data values pull on the mean. We can think of it like a tug-of-war.