Question

if two numbers are selected from 20 concentrative numbers. Find the probability that the sum of two numbers ​

Answer 1

if there are two numbers then there sum will one number and also there are total 20 numbers. So probability is 1/20

Answer 2

10C  

2

​  

=  

2×1

10×9

​  

=45odd

10C  

2

​  

=  

2

10×9

​  

=45odd

20C  

2

​  

 

10C  

2

​  

+10  

2

​  

 

​  

=  

20×19

45+45

​  

=  

190

90

​  

=  

19

9

​  

Ans.

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