In a class,$70 \%$ of the students read Hindi,$40 \%$ of the students are boys,and $20 \%$ of the girls do not read Hindi. What percentage of boys read Hindi?

An engineering student has to secure $25 \%$ marks to pass. He gets $47$ marks and fails by $43$ marks. What are the maximum marks of the examination?

Two numbers are less than a third number by $30 \%$ and $37 \%$ respectively. How much per cent is the second number less than the first (in $\%$)?

If the price of a shirt is increased by $25 \%$ and then decreased by $30 \%$,then what will be the net effect?

$A$ jar contains $10$ red marbles and $30$ green ones. How many red marbles must be added to the jar so that $60 \%$ of the marbles will be red?

In a motor of $120$ machine parts,$5 \%$ parts were defective. In another motor of $80$ machine parts,$10 \%$ parts were defective. For the two motors considered together,the percentage of defective machine parts was (in $\%$)