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The average of 8 numbers is 20. The aver...

The average of 8 numbers is 20. The average of first tow numbers is 15 `(1)/(2)` and that of the next three is `21 (1)/(3)`. If the sixth number be less that the seventh and eight numbers by 4 and 7 respectively, then the eighth number is :

A

18

B

22

C

25

D

27

Text Solution

Verified by Experts

The correct Answer is:
C
आठ संख्याओं का योग `=20xx8=160`
प्रथम पाँच संख्याओं का योग `=((31)/(2)xx 2 ) + ((64)/(3) xx 3) = 95`
माना कि छठवीं संख्या =x
अब प्रश्न से, 95 +(x +x+4+x+7) = 160
`implies 3x +11=65`
` implies 3x=54`
`:.`x=18
`:.` आठवीं संख्या = 18 +7=25
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