UPSC 2016 CDS II Math Paper

Let the old average of the cricketer be n.
∴ New average of the cricketer
=n+6
Total runs scored by the cricketer in 10 innings = 10n
Total runs scored by the cricketer in 11 innings =10n+108
∴11(n+6)=10n+108
⇒11n–10n=108–66
⇒n=42
∴ New average of the cricketer=42+6=48