The average of twelve numbers is 42 . The average of the last five numbers is 40 , and that of the first four numbers is 44 . The sixth number is 6 less than the fifth number and 5 less than the seventh number. The average of the sixth and seventh numbers is:
Answer & explanation
Correct answer: option 1
Sum of 12 numbers = 12 x 42 = 504
Sum of last five numbers = 5 x 40 = 200
Sum of first four numbers = 4 x 44 = 176
Sum of 5th, 6th and 7th number = 504 - 200 - 176 = 130
Let 6th number be x
5th number be x + 6
7th number be x + 5
⇒ 3x + 11 = 128
⇒ x = 39
Average of 6th and 7th = \(\frac{39 + 44}{2}\) = 41.5