header bg

Question:

A set of 9 numbers {3, 3, 4, 5, 5, 5, 6, 7, 7} has a mean of 5. Another number is added to the set and the mean becomes 6.
What number is added to the set?

A 15
Explaination

The total sum of the 9 numbers is $5116_w82_h14.png$
The total sum of the 10 numbers is $1953_w90_h13.png$
45 + number added = 60.
Number added is 60 - 45 = 15.