Question

The average age of 30 boys in a class is 15.2 yr. If 15 more boys join the class, the average age of the class is reduced by half a year. The average age of newcomers is 

विकल्प

• 13.0yr

• 12.3yr

• 13.7 yr

• 14.0 yr

Answer 1

13.7 yr

Explanation:
The average age of 30 boys = 15.2 yr
∴ Total age of 30 boys = 15.2 x 30 = 456 yr
15 more boys join the class then total number of boys 
 = 30 + 15 = 45
Let total age of 45 boys = x
Then, according to question,

`"x"/45 = 15.2 - 1/2` yr

⇒  `"x"/45 = 15.2 - 0.5`

⇒  x = 14.7 × 45 = 661.5 yr

Now,
the average age of newcomers = `(661.5- 456)/15` =` 205.5/15=13.7`yr