# IIT JEE 1982 Maths - 'Adapted' - Subjective to Multi-Correct Q10

Algebra Level pending

$f(n)=\frac{1}{1+\sqrt2}+\frac{1}{\sqrt2+\sqrt3}+\frac{1}{\sqrt3+2}+...+\frac{1}{\sqrt{n-1}+\sqrt{n}}$

For $$f(n)$$ as defined above, which of the following options are correct?

• A: $$f(10)=2$$
• B: $$f(15)=3$$
• C: $$f(20)=4$$
• D: $$f(25)=5$$

Enter your answer as a 4-digit string of 1s and 9s $$-$$ 1 for correct option, 9 for wrong. For example: if A and B are correct, and C and D are incorrect, enter 1199. None, one or all may also be correct.

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