Sum of all the 13 numbers = 13 * 60 = 780
Sum of the first 7 of them = 7 * 55 = 385
Sum of the last 7 of them = 7 * 61 = 427
So, the 8th number = 427 + 385 - 780 = 32.
The average of 13 numbers is 60. Average of the first 7 of them is 55 and that of the last 7 is 61. Find the 8th number?
a: 32
b: 83
c: 45
d: 53
e: 64