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Option 2 : 18th person

⇒ The donation made by everyone is in the form of squares of integers.

Assume that donation made by nth person surpasses the tally of 2000 Rs.

⇒ 12 + 22 + 32 + 42 + ......... + n2 > 2000

⇒ n/6 × (n + 1)(2n + 1) > 2000

By Hit and Trial,

⇒ Try for n = 17

n/6 × (n + 1)(2n + 1) = 17/6 × (18) (35) = 1785 < 2000

⇒ Now, try n = 18

n/6 × (n + 1)(2n + 1) = 18/6 × (19)(37) = 2109 > 2000

Hence, donation made by 18th person will surpass the tally of Rs. 2000.
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