$20 \%$ loss on selling price is what per cent loss on the cost price? (in $\%$)

Nutan bought $30$ dozens of oranges for her juice stall in the school fair. She paid $Rs. 8$ per dozen of oranges. She also had to pay $Rs. 500$ as the stall fee to the school authorities. She calculated that each glass of juice would need $3$ oranges. How much should she charge per glass of juice so as to make $20 \%$ profit in $Rs$?

$A$ shopkeeper mixes $26 \, kg$ of wheat which costs $Rs. 20$ per $kg$ with $30 \, kg$ of wheat which costs $Rs. 36$ per $kg$ and sells the mixture at $Rs. 30$ per $kg$. Find the profit percent. (in $\%$)

If a radio is purchased for $Rs. 490$ and sold for $Rs. 465.50$,find the $\text{loss} \%$. (in $\%$)

The marked price of a watch was $Rs. 720$. $A$ man bought the same for $Rs. 550.80$ after getting two successive discounts,the first being $10\%$. What was the second discount rate? (in $\%$)

$A$ dishonest dealer uses a scale of $90 \, cm$ instead of a metre scale and claims to sell at cost price. His profit percentage is: