The average age of an adult class is 40 years. 12 new students with an average age of 32 years join the class. Therefore decreasing the average by 4 year. what was the original strength of class?

10
11
12
15

Correct Answer: 12

Explanation:

Let original strength = y
Then , 40y + 12 x 32 = ( y + 12) x 36
⇒ 40y + 384 = 36y + 432
⇒ 4y = 48
∴ y = 12

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