In a class, the average age of 28 boys is 13 years. Two boys whose ages are 'x' years and 21 years leave the class. If the new average age of the class is 13 years, then what is the value of 'x'?

Correct option is B

Given:
Initial number of boys = 28
Initial average age = 13 years
Ages of the two boys who left = 'x' years and 21 years
New average age after they leave = 13 years
Formula Used:
Total Age = Average Age × Number of individuals
Solution:
The initial total age of the 28 boys is:
28 × 13 = 364
Two boys leave, so the new number of boys is 26. Their new average is still 13 years.
The new total age of the 26 boys is:
26 × 13 = 338
The difference between the initial total age and the new total age gives the sum of the ages of the two boys who left.
Age sum = 364 - 338 = 26
Therefore, the sum of 'x' and 21 must equal 26.
x + 21 = 26
x = 5
Final Answer
So the correct answer is (b)