The average of ten numbers is 72. The average of the first four numbers is 69 and that of the next three numbers is 74. The 8th number is 6 more than the 9th number and 12 more than the 10th number. What is the average of the 8th and 9th numbers?
Answer & explanation
Correct answer: option 4
Sum of all ten numbers= 72 x 10 = 720
Sum of first four numbers = 69 x 4 = 276
Sum of next three numbers = 74 x 3 = 222
Sum 8th, 9th & 10th number = 222
Lets assume 8th number is x then 9th & 10th numbers are x - 6 & x - 12
So, 3x - 18 = 222
x= 80
Accordingly, 8th & 9th numbers are 80 and 74
Avg. = 77