Question

1×3×5×7.............99 ka ikai ank kya hoga

Answer 1

I will use P(1 - n) to mean the product of numbers from 1 to n. 

You want to find P(1 ∙ 3 ∙ 5 ∙ 7 . . . . . 99) 

which is obviously 

99! - P (2 ∙ 4 ∙ 6 ∙ 8 . . . . . 98) 

= 99! - P(1 ∙ 2 ∙ 3 ∙ 4 ∙ . . . . .49) ∙ 2^49 . . . . . (take out a factor of 2 from each of 2, 4, 6, etc.) 

= 99! - (49!) (2^49)

Answer 2

(n-1)/2

n=99
99-1/2= 49