Average Practice Test 3

Question : 34 of 40

Marks: +1, -0

The average of 8 numbers is 20. The average of first two numbers is

15 1/ 2

and that of the next three is

21 1 /3

. If the sixth number be less than the seventh and eighth numbers by 4 and 7 respectively, then the eighth number is:

Solution:

Let the sixth, seventh and eighth numbers are x, x + 4 and x + 7.
Sum of last three numbers

= 8 × 20 - (2 × 31/ 2+ 3 ×64/ 3 )

⇒ x + x + 4 + x + 7= 160-95

⇒ 3x + 11 = 65

⇒3x = 54

⇒ x = 18

New eighth number = x + 7 = 18 + 7 = 25

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