The average age of 40 students of class is 18 years. When 20 new students are admitted to the same class, the average age of the students of the class is increased by 6 months. The average age of newly admitted students is ?

According to the question,
Average age of 40 students of class is = 18 years
Let the average age of 20 new students = x years
∴ $$\frac{40 × 18 + 20 × x}{60}$$   = $$\left( {18 + \frac{1}{2}} \right)$$  years
⇒ $$\frac{720 + 20x}{60}$$   = $$\frac{37}{2}$$
⇒ $$\frac{720 + 20x}{30}$$   = 37
⇒ 20x = 390
⇒ x = 19.5
∴ Average age of newly admitted students is
= 19.5 = 19 years 6 months