The $CP$ of $19$ articles is equal to the selling price $(SP)$ of $15$ articles. What is the gain percentage?

$A$ cab driver makes a profit of $20 \%$ on every trip when he carries $3$ passengers and the price of petrol is $Rs. 30$ a litre. Find the percentage profit for the same journey if he goes with four passengers per trip and the price of petrol reduces to $Rs. 24$ a litre? (in $\%$)
(Assume that revenue per passenger is the same in both the cases.)

$A$ man buys an article for $10 \%$ less than its value and sells it for $10 \%$ more than its value. His gain or loss percent is

$A$ shopkeeper sold decks at $Rs. 166$ each after giving $17\%$ discount on the labelled price. Had he not given the discount,he would have earned a profit of $25\%$ on the cost price. What was the cost price of each deck? (in $Rs.$)

Sudeep buys two $CDs$ for $Rs. 380$ and sells one at a loss of $22 \%$ and the other at a gain of $12 \%$. If both the $CDs$ are sold at the same price,then the cost price of the two $CDs$ is (in $Rs.$)

$A$ shopkeeper gains the cost of $8$ metres of thread by selling $40$ metres of thread. Find his gain percent.