A trader purchase a wrist watch and a pendulum for $Rs.$ $390.$ He sells them making a profit of $10 \%$ on the watch and $15 \%$ on the pendulum. He earns a profit of $Rs$. $51.50 .$ The difference between the original prices of the pendulum and the watch is equal to? (in $Rs.$)

Successive discounts of $10 \%, 20 \%$ and $50 \%$ will be equivalent to a single discount of..........$\%$

If on selling $12$ note books, a seller makes a profit equal to selling price of $4$ notebooks. What is his percent profit?

A pen was sold for a certain sum and there was a loss of $20 \% .$ Had it been sold for $Rs.\, 12$ more, there would have been a gain of $30 \% .$ What would be the profit if the pen was sold for $Rs.\, 4.80$ more than what it was sold for? (in $\%$)

A vendor buys bananas at $9$ for $Rs. 8$ and sells at 8 for $Rs. 9.$ What will be the profit or loss (in $\%$)?

A plate was sold for $Rs.\,6,300$ after giving two successive discounts of $12^{1 / 2} \%$ and $10 \% .$ Find the marked price. (in $Rs.$)