The average of 8 numbers is 20. The average of first two numbers is $$15\frac{1}{2}$$ and that of the next three is $$21\frac{1}{3}$$. 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 Examveda Team)
Let the eight number be xThen, sixth number = (x - 7)
Seventh number = (x - 7) + 4 = (x - 3)
So,
$$ \Leftrightarrow \left( {2 \times 15\frac{1}{2}} \right) + \left( {3 \times 21\frac{1}{2}} \right)$$ $$ + \left( {x - 7} \right)$$ $$ + \left( {x - 3} \right)$$ $$ + \,x = 8 \times 20$$
$$\eqalign{ & \Leftrightarrow 31 + 64 + \left( {3x - 10} \right) = 160 \cr & \Leftrightarrow 3x = 75 \cr & \Leftrightarrow x = 25 \cr} $$
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Comments ( 1 )
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My doubt is right no is by 4 and 7 means I didn't get plz clearly explain the strp