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Question

a bag contains $3$ red, $6$ white and $7$ blue balls. What is the probility that two balls drawn are white and blue?

2016-12-21 11:47:29

Sanjay Kumar
1 Answer

**Solution 1**

Number of ways in which two balls can be selected

$=16\text{C}2=120$

Number of ways in which one white ball and one blue ball can be selected

$=6\text{C}1×7\text{C}1 =42$

Required probability $=\dfrac{42}{120}=\dfrac{7}{20}$

**Solution 2**

P(first ball white and second ball blue)

$=\dfrac{6}{16}×\dfrac{7}{15}=\dfrac{42}{240}$

P(first ball blue and second ball white)

$=\dfrac{7}{16}×\dfrac{6}{15}=\dfrac{42}{240}$

Required probability $=\dfrac{42}{240}+\dfrac{42}{240}=\dfrac{7}{20}$