∴ The probability that the first ball is even numbered =  10 
21 
Since the ball is not replaced there are now 20 balls left, of which 9 are even numbered.
∴ The probability that the second ball is even numbered =  9 
20 
∴ Required probability =  10  ×  9  =  9  =  3 
21  20  42  14 
E_{1} =  3  =  1 
12  4 
E_{2 } =  5  =  5 
12  12 
=  1  +  5  =  2 
4  12  3 
1  ×  1  ×  16  =  2 
2  2  50  25 
∴ The required probability =  1 
4 
= 

= 

= 


