Correct Answer - Option 3 : 20
Given:
Initial average = 16.75 years.
20 new persons with an average age of 13.25 years joined
New average = 15 yrs.
Formula:
Average of n numbers a1, a2, ………. an = (a1 + a2 + ... + an)/n
Calculation:
Let the no. of person initially going for the trip be x.
Total age of x persons = x × 16.75
Total age of 20 persons = 13.25 × 20 = 265
Total age of all the persons = 15 × (x + 20)
From the question
16.75x + 265 = 15(x + 20)
⇒ 16.75x + 265 = 15x + 300
⇒ 1.75x = 35
⇒ x = 20
∴ Initial number of person is 20
