The exact conclusion cannoty be derived unless we know AUB or AIntersectionB.
AUB= A+B-AintersectionB.
we know A+B=51+49 as mentioned ...
So there are three subsets now .. 1 who only trade NIFTY ..2 Who only trade stocks and 3 Who trade both.
So this can be through various possiblilities
But most likely in our case 49% trading in stocks are also trading Nifty ..
So deducting it from 51% ... there are only 2% who trade ONLY NIFTY .. ONLY STOCKS 0% and BOTH 49%.
CAT yaad aagaya ...