If using equations is difficult then take sample numbers.
Lets say X = 300, S = 100, F=200 and B = 50.
Neither will come as 50. (which is nothing but X+B -F-S).
Substitute these values in the equations. Only D will give the value as 50/300 *100 (as its percent).
PareshGmat wrote:
Answer = D. 100*(X + B - F - S)/X
Refer diagram below. We require to find the pink colour region percentage of total x
Attachment:
venn.png
Total x = s + f-b + {Neither}
{Neither} = x - s - f + b
Percentage \(= \frac{100}{x} * (x - s - f + b)\)