THe average of twelve number id 39, the average of the last five number is 35, and that of the first four number is 40. The fifth number is 6 less than sixth number and 5 more than the seventh number. The average of the fifth and sixth number is :
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 47
The average of twelve numbers = 39
The average of the last five numbers = 35
The average of the first four numbers = 40
The fifth number is 6 less than the sixth number and 5 more than the seventh number.
Sum = Average × total number
The Sum of the twelve numbers = 12(39) = 468
The sum of the last five number = 5(35) = 175
The sum of the first four number = 4(40) = 160
The sum of the fifth, sixth and seventh number = (468 - 175 - 160) = 133
Let the fifth number be x
The sixth number = (x + 6)
The seventh number = (x – 5)x + (x + 6) + (x – 5) = 133
3x + 1 = 133
3x = 132
x = 44
The fifth number = 44
The sixth number = (44 + 6) = 50
Average of fifth and sixth number = (44 + 50)/2 = 47