The average age of 12 students is 20 years. If the age of one more student is included, the average decreases by 1. What is the age of the new student?

One Answer on this Question

1. Correct option is C)
   Let be students are consider as child
   Let the age of child added later be x years.
   average age of 12 children =20 years
   ∴ Total age of 12 children =20×12=240 years
   After one more child is added-
   Average of 13 children =20−1=19 years
   Average age of 13 children =
   13
   sum of 12 children+x
   ​

   19=
   13
   240+x
   ​

   ⇒240+x=247
   ⇒x=247−240=7 years
   Hence the age of child added later is 7 years.

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