The average of eleven numbers is 68. The average of the first four numbers is 78 and that of the next four numbers is 63. The 9th number is two times the 11th number and the 10th number is less than the 11th number. What is the average of the 9th and 11th numbers?

70.5

Sum of 11 numbers = 68 x 11 = 748

Sum of 4 numbers = 78 x 4 = 312

Sum of next 4 numbers = 63 x 4 = 252

Sum of 9th, 10th and 11th numbers = 748 - 312 - 252 = 184

Lets assume 11th number be x

9th number = 2x

10th number = x - 4

x + 2x + x - 4 = 184

x = 47

11th number = 47

9th number = 94

Average of 9th and 11th number = 70.5