By selling $33$ metres of cloth a man gains the cost price of $11$ metres of cloth. Find his gain percent.

Selling $33$ m at SP minus their CP equals the CP of $11$ m: Gain on $33$ m $=$ CP of $11$ m. Gain $\% = \dfrac{\text{Gain}}{\text{CP of 33 m}} \times 100 = \dfrac{11}{33} \times 100 = 33\tfrac{1}{3}\%$. A common slip is to divide by $44$ instead of $33$ — but the CP base is the $33$ metres actually sold.