If a commission of 10% is given on the written price of an article, the gain is 20%. The gain per cent, when the commission is increased to 20%, will be?

Let MP of the article = ₹ N
∴ SP of the article = N x (100 - 10)/100 = ₹ 9N/10
⇒ CP of the article = [(9N/10) x 100]/(100 + 20)
= (9N x 10)/120
= ₹ 3N/4
Now, new SP of the article = [N x (100 - 20)]/100 = ₹ 4N/5
New profit = 4N/5 - 3N/4 = (16N - 15N)/20 = ₹ N/20
Hence, profit per cent = [(N/20) / (3N/4)] x 100 %
= (4 x 100)/(3 x 20) %
= 6²/₃%