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

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}

A. 20
B. 21
C. 28
D. 32

A. 18
B. 20
C. 24
D. 30

A. 10 years
B. 10.5 years
C. 11 years
D. 12 years