Permutation Combination in Numbers

Question 1
a, b, c are three positive integers (not necessarily distinct) that add up to give 11. How many such combinations of a, b and c exists?

1. 150
2. 55
3. 120
4. 45

Correct Answer is 45. Choice (D)

Explanatory Answer

Imagine 11 1s placed in a straight line.

Imagine we now place two "+" symbols in 2 slots somewhere in between these 1s.

The answer to the question would be the same as the number of ways in which we can place the 1s or ¹⁰C₂ or 45.

Answer is Choice D.

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AIEEE Math Problems, Practice Questions and Answers : Listed Topicwise

Sets, Relations & Functions		Permutation Combination		Sequences & Series
Limits, Continuity & Differentiability		Statistics & Probability		Trigonometry
Mathematical Reasoning