If the selling price of an article is $\frac{4}{3}$ of its cost price,the profit percentage in the transaction is: (in $\%$)

If the ratio of the cost price and selling price of an article is $20: 21$,then what will be the profit percent (in $\%$)?

By selling a fan for $Rs. 1900$,a man has a loss of $5 \%$. At what price (in $Rs.$) should he sell the fan to gain $20 \% ?$

$A$ person sold a radio at a loss of $5 \%$. Had he sold it for $Rs. 210$ more,he would have gained $25 \%$. For what value should he sell it in order to gain $35 \%?$

$A$ man sold two cows at $Rs. 1995$ each. On one he lost $10\%$ and on the other he gained $10\%$. What is his gain or loss percent (in $\%$)?

$A$ sold a pen to $B$ at a profit of $20\%,$ $B$ sold the same pen to $C$ for $Rs.\,75$ thereby making a profit of $25 \% .$ Find the price at which $A$ bought the pen? (in $Rs.$)