A bag holds four green, three red and two yellow marbles. Two are drawn without replacement. Once a yellow is drawn first, how many marbles remain?
ANine marbles
BSeven marbles
CFour marbles
DEight marbles
Answer & Solution
Correct answer: D. Eight marbles
1. Add the marbles up first: 4 green plus 3 red plus 2 yellow.
2. That is 9 marbles in the bag to start with.
3. Drawing without replacement means the first marble is not put back.
4. So one marble leaves the bag.
5. 9 minus 1 is 8 marbles remaining.
6. The four green marbles are all still there, which is why the second chance is four out of eight.
7. Answering nine forgets that the drawn marble was kept out.
_Source: OpenStax High School Statistics (CC BY 4.0), Ch 2 "Descriptive Statistics" and Ch 3 "Probability Topics", section 3.3 Two Basic Rules of Probability_
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