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Quantitative Aptitude(IBPS RRB PO)

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The average age of group of persons going for picnic is 16 years. Twenty new persons with an average age of 15 years join the group on the spot due to which their average becomes 15.5 years. Find the number of persons initially going for picnic.

Explanation:

Average age of 'n' number of persons = 16
Total age of 16 persons = 16n
Number of men after increase = (n + 20)
Average age of (n + 20) men = 15.5
Total age of (n + 20) men = (n + 20) x 15.5
Average age of 20 men = 15
Total age of 20 men = 20 x 15 = 300
⇒ (n + 20) x 15.5 = 16n + 300
⇒ 15.5 n + 310 = 16n + 300
⇒ 10 = 0.5 n
⇒ n = 20

Hence, option 2 is the correct answer.

By: Amit Kumar

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