What is $15$ percent of $ 34$?

If in an examination $20 \%$ students failed in Hindi,$25 \%$ failed in English,and $7 \%$ failed in both subjects,then what is the percentage of students who failed in at least one of the subjects (in $\%$)?

If a number multiplied by $25 \%$ of itself gives a number which is $200 \%$ more than the number,then the number is:

In an examination,$65 \%$ of students pass in History and $55 \%$ of students pass in Hindi. If $5 \%$ of students fail in both subjects,what is the percentage of students who passed in both subjects?

$A$ number is increased by $84$,it becomes $107 \%$ of itself. What is the number?

$A$ fruit seller had some apples. He sells $40 \%$ of the apples and still has $420$ apples. Originally,how many apples did he have?