Question 692309
The average of the first 3 numbers = S3/3 = 11 -> S3 = 33 
where S3 = the sum of the first 3 numbers
The average of the other 7 numbers = S7/7 = 12 -> S7 = 84
So the overall average = (S3+S7)/10 = (33+84)/10 = 11.7