The average of twelve numbers is 45.5. The average of the first four numbers is 41.5 and that of the next five numbers is 48. The 10^th number is 4 more than the 11^th number and 9 more than the 12^th number. What is the average of the 10^th and 12^th numbers?

46.5

Sum of all 12 numbers= 12 x 45.5 = 546

Sum of first four numbers = 41.5 x 4 = 166

Sum of next Five numbers = 48 x 5 = 240

Sum 8th, 9th & 10th number = 140

Lets assume 10th number is x then 11th & 12th numbers are x - 4 & x - 9

So, 3x - 13 = 140

x = 51

Accordingly, 10th & 12th numbers are 51 and 42

Avg. = 46.5