The average of 8 numbers is 20. The average of first two number 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 number by 4 and 7 respectively, than the eighth number is :
Let the eighth number be `x`. Then sixth number = (`x` -7)
seventh number = (`x` - 7) + 4 = `x` -3
so `(2 xx 15 1/2)` + `(3 xx 21 1/3)` + (`x` - 7) + (`x` - 3) + `x` = 8 x 20
`hArr` 31 + 64 + `3x` - 10 = 160 `hArr` 3`x` = 75 `hArr` `x` = 25
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