20 छात्राओ की औसत आयु 15 वर्ष है तथा 25 छात्रो की औसत आयु 24 वर्ष है, तो छात्र तथा छात्राओ की औसत आयु ज्ञात करे?

Options

A. 19.5 years
B. 20 years
C. 21 years
D. 21.5 years

Answer

B

Explanation

According to the question
The average age of 20 girls is =15 years
The average age of 25 boys is = 24 years
`therefore` Mixed average
`=(20xx15+25xx24)/45=(300+600)/45`
`=900/45=20` years
Alternate : By using alligation method.

9 divides in 4 :5 are 4 and 5
`therefore` Average age = 20 years