$8$ litres of water is added to $32$ litres of a solution containing $20 \%$ of alcohol in water. What is the approximate concentration of alcohol in the solution now? (in $\%$)

$300$ $grams$ of sugar solution contains $40 \%$ sugar. How much sugar should be added to make the concentration $50 \%$ in the solution? (in $grams$)

$20$ litres of a mixture contains $20 \%$ alcohol and the rest is water. If $4$ litres of water are added to it,what will be the percentage of alcohol in the new mixture?

An amount of ₹ $70,000$ was lent at $6 \%$ per annum and the remaining at $4 \%$ per annum. If the total simple interest from both the fractions in $5 \text{ years}$ was ₹ $16,000$,the sum lent at $6 \%$ per annum was (in ₹). (in $,000$)

$A$ cylinder which has the capacity of $8 \text{ litres}$ contains a mixture of oxygen and nitrogen. The volume of oxygen in the cylinder is $16 \%$ of the total volume. $A$ few litres of the mixture is released and an equal amount of nitrogen is added. Then,the same amount of the mixture as before is released and replaced by nitrogen for the second time. As a result,the oxygen content becomes $9 \%$ of the total volume. Find the amount of mixture released each time (in litres).

In what ratio should sugar at ₹ $30$ per $kg$ be mixed with sugar at ₹ $45$ per $kg$ so that on selling the mixture at ₹ $42$ per $kg$ there is a profit of $20 \%$?