# Jane Street FTTP & INSIGHT

## A rule change moves the answer

Original probability exercise, not an employer assessment.

### Two draws from three red and two blue counters

| Sampling rule | Red then blue | Blue then red | Different colors |
| --- | --- | --- | --- |
| Without replacement | 3/5 × 2/4 = 0.30 | 2/5 × 3/4 = 0.30 | 0.60 |
| With replacement | 3/5 × 2/5 = 0.24 | 2/5 × 3/5 = 0.24 | 0.48 |

## Your turn

Explain the change without relying on a memorized answer. Name a software test or process check that would prevent the rules from being confused.

## Your answer

[Write your approach here.]

## For your own application

Practice explaining one small problem completely, including the assumption that makes your answer valid.

Return to the guide for the worked answer and source notes:
https://internshipdeadlines.com/guides/jane-street-fttp-insight-programs-guide