Q.

Two distinct numbers a and b are selected at random from 1,2,3,,50. The probability that their product ab is divisible by 3, is         [2026]

1 6641225  
2 5611225  
3 825  
4 2721225  

Ans.

(1)

Required probability=1-(product not divisible by 3)

Multiple of 3=16

Not multiple of 3=34

=1-C234C250

=6641225