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The average of 8 numbers is 20. The average of first two numbers is $15 \Large\frac{1}{2}$ and that of the next three is $21 \Large\frac{1}{3}$. If the sixth number be less than the seventh and eighth numbers by 4 and 7 respectively, then the eight number is-

A. 18 B. 22 C. 25 D. 27 Answer: Option C
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Solution(By Apex Team)

Let the eight number be x Then, sixth number = (x – 7) Seventh number = (x – 7) + 4 = (x – 3) So, $\begin{aligned}&\Leftrightarrow\left(2\times15\frac{1}{2}\right)+\left(3\times21\frac{1}{2}\right)+(x-7)+(x-3)+x=8\times20\\ &\Leftrightarrow31+64+(3x-10)=160\\ &\Leftrightarrow3x=75\\ &\Leftrightarrow x=25\end{aligned}$

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