Correct option is B
Shyam purchased a packet of 16 pens and got 4 pens free with it
Marked percentage = 20%
Selling price = Marked price
SP = CP × [(100 + Profit%)/100]
Discount = free item/Total item × 100
Let the cost price of 16 pens and getting 4 pens free with it be Rs. 100x
Discount = free item/Total item × 100
= 4/20 × 100
= 20%
Shyam's C.P = 100x × 80/100
= 80x
Marked price = 100x × 120/100
= 120x
M.P = S.P
Profit% = (120x - 80x)/80x × 100
= 50%