BYSELLING 33m OF CLOTH, ONE GAINS THE SELLING OF 11m . THE GAIN PERCENT IS

Let us assume the selling price = Rs1/meter
The man sold for 33m hence, for  Rs 33
He gained money equal to the dollar value of 11m, hence Rs 11.

Since, profit = Selling price - cost price, hence, cost = selling price - profit = Rs (33-11) = Rs 22 
profit % = Profit/cost *100 = 11/22 * 100 = 50%