Answer should be (C)
Let ,In old design , Total Marbles = 100
So , Number of blue,black,red and yellow marbles should be 40,25,20,15 respectively.
Let cost of each marble = x . So , Total cost for 100 marbles in old design = 100x
Now, For new design , Let we reduce 't' marbles from each blue , black,red and yellow marbles of old design.
So, In new design ,number of blue , black, red and yellow marbles should be (40-t) , (25-t) ,(20-t) , (15-t) respectively.
Now ,According to question , cost of each marble is increased by 25% . So , In new design , cost of each marble will be x + (25/100)*x = 5x/4. So, here , Total cost = [(40-t) + (25-t) + (20-t) + (15-t) ]*(5x/4) = (100 - 4t)*(5x/4)
Now , According to given condition cost of old design of marbles = cost of new design of marbles
So, 100x = (100 - 4t)*(5x/4) .After solving, we get t = 5
So , In new design , number of blue,black,red and yellow marbles will be (40-5) , (25-5) ,(20-5) , (15-5) ie. 35,20,15,10 respectively.
So, here , Total marbles = 80 and blue marbles = 35 . So , % of blue marbles = (35/80)*100 = 43.75