SSC Sample Paper Mock Test-6 SSC CGL Tear-II Paper-1

The average of eight numbers is 20. If the sum of first two numbers is 31, the average of the next three numbers is \[21\frac{1}{3}\] and the seventh and eighth numbers exceed the sixth number by 4 and 7 respectively, then the eighth number is

A) 20

B)                    25

C) 21.6

D) 25.3

Correct Answer: B

Solution :

\[\therefore \] Required Average age\[=\frac{96}{3}=32\,\,\text{yr}\]

Sum of the eighth numbers \[=20\times 8=160\]

Sum of the first two numbers = 31

Sum of the next three numbers \[=\frac{64}{3}\times 3=64\]

Let the sixth number \[=x\]

\[\therefore \] Seventh number \[=x+4\]

and eighth number \[=x+7\]

\[\therefore \] \[31+64+x+x+4+x+7=160\]

\[\Rightarrow \] \[3x+106=160\]

\[\Rightarrow \] \[3x=160-106=54\]

\[\Rightarrow \] \[x=\frac{54}{3}=18\]

\[\therefore \] Eighth number \[=x+7=18+7=25\]