Add a number in 1,2,3,4,5,6,7,8,9,10, so that the average number of the group is 6, then what is the increased number?

Add a number in 1,2,3,4,5,6,7,8,9,10, so that the average number of the group is 6, then what is the increased number?

11, the sum of these ten numbers equals 55. So if the average number of 11 numbers is 6, it's OK for them to add up to 66. 66-55 = 11