Try this beautiful problem from Probability based on Positive factors

## Probability – AMC-10A, 2003- Problem 8

What is the probability that a randomly drawn positive factor of \(60\) is less than \(7\)?

- \(\frac{1}{3}\)
- \(\frac{1}{2}\)
- \(\frac{3}{4}\)

**Key Concepts**

Probability

Factors

combinatorics

## Check the Answer

Answer: \(\frac{1}{2}\)

AMC-10A (2003) Problem 8

Pre College Mathematics

## Try with Hints

Now at first we find out the positive factors of \(60\) are \(1,2,3,4,5,6,10,12,15,20,30,60\).but the positive factors which are less than \(7\) are \(1,2,3,4,5,6\)

Can you now finish the problem ……….

so we may say that any For a positive number \(n\) which is not a perfect square, exactly half of the positive factors will be less than \(\sqrt{n}\).here \(60\) is not a perfect square and \(\sqrt 60 \approx 7.746\).Therefore half of the positive factors will be less than \(7\)

can you finish the problem……..

Therefore the required probability=\(\frac{1}{2}\)

## Other useful links

- https://www.cheenta.com/area-of-triangle-problem-amc-10a-2009-problem-10/
- https://www.youtube.com/results?search_query=cheenta