abhi.genx7 wrote:Q2 ) A bag contains 3 white balls, 3 black balls & 2 red balls. One by
one three balls are drawn out without replacement. What is the
probability that the third ball is red?
Answer Choices
0.15
0.25
0.35
0.40
0.45
1. Draw a diagram:
3W, 3B, 2R in a bag. Literally draw the bag and mention the same inside it. Then check what you are asked
third one has to be Red _ _
R. (Must)
2. Check all possible scenarios:
XRR : 3rd pick is bound to be RED, First one can be anything so X, If you pick second as RED then there will be a change in the situation
RXR : 3rd pick is bound to be RED, Second one can be anything so X, If you pick First as RED then there will be a change in the situation
XXR: First two can be anything except RED and 3rd pick is bound to be RED.
Dont agree with me... you think why no more scenarios and though 1 and 2 seem same why I am showing 2 scenarios.
3. When one is happening AND other is happening MULTIPLY.
These 3 events are happening one after another. Means in XRR: X happened AND R happened and R happened.
XRR = [6/8 * 2/7 * 1/6]
RXR = [2/8 * 6/7 * 1/6 ]
XXR = [6/8 * 5/7 * 2/6]
You figure out why 6/8 why 2/7 why 1/6...etc.
4. When one happens OR other happens ADD.
Now from the above 3 scenarios one is going to happen not all 3. Right!!
Either XXR OR XRR OR RXR
Thus adding the values from 3 you will get 0.25
Hope this helps
