Let the total number of pens be '100n'. Let the cost price of a pen be Rs. '10a' So, marked price of a pen = 10a X 1.4 = Rs. '14a' So, the cost price of all pens = 100n X 10a = Rs. '1000na' ATQ, Selling price of 70% of total number of pens = 0.7 X 100n X 14a = Rs. '980na' Selling price of remaining pens = 0.3 X 100n X 10a X 1.4a X 0.8 = Rs. '336na' Total selling price = 980na + 336na = Rs. '1316na' Therefore, required profit = (1316na - 1000na) ÷ 1000na X 100 = 31.6%