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Question: Answered & Verified by Expert
An urn contains one black ball and one green ball. A second urn contains one white and one green ball. One ball is drawn at random from each urn.
What is the probability of getting at least one green ball?
MathematicsProbabilityNDANDA 2012 (Phase 2)
Options:
  • A $1 / 2$
  • B $1 / 3$
  • C $2 / 3$
  • D $3 / 4$
Solution:
2765 Upvotes Verified Answer
The correct answer is: $3 / 4$
Total number of balls in urn $-\mathrm{I}=1$ Black $+1$ Green $=2$ Balls Total number of balls in urn $-\mathrm{II}=1$ White $+1$ Green $=2$ Balls
$\begin{aligned} \text { Required prob }=(1 \mathrm{G})_{\mathrm{I}} \times(1 \mathrm{G})_{\mathrm{I}}+(1 \mathrm{G})_{\mathrm{I}} \times(1 \mathrm{~B}) \mathrm{I} \\ &+(1 \mathrm{G})_{\mathrm{II}} \times(1 \mathrm{~W})_{\mathrm{II}} \\=\left(\frac{1}{2} \times \frac{1}{2}\right)+\left(\frac{1}{2} \times \frac{1}{2}\right)+\left(\frac{1}{2} \times \frac{1}{2}\right)=\frac{1}{4}+\frac{1}{4}+\frac{1}{4}=\frac{3}{4} \end{aligned}$

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