Project ForgeEngineering Mathematics
Probability & Statistics
GATE 2010
Medium
A box contains three red and two black balls. Four balls are removed from the box one by one, without replacement. The probability of the ball remaining in the box being red, is
- A609/625
- 3/5
- C2/5
- D81/625
Explanation
By symmetry, each of the 5 balls is equally likely to be the one left remaining after 4 are drawn without replacement. So P(remaining ball is red)=3/5 (the fraction of red balls).
Source: GATE CH 2010 (2010)
This question is part of a 15-day revision cycle — sign in and Project Forge will bring it back the day before you'd forget it.