Two alloys contain tin and iron in the ratio of $1:2$ and $2:3$. If the two alloys are mixed in the proportion of $3:4$ respectively (by weight),the ratio of tin and iron in the newly formed alloy is:

$A$ sum of $Rs. 6.40$ is made up of $80$ coins which are either $10$-paise or $5$-paise coins. How many $5$-paise coins are there?

$A$ barrel contains a mixture of wine and water in the ratio $3:1$. How much fraction of the mixture must be drawn off and substituted by water so that the ratio of wine and water in the resultant mixture in the barrel becomes $1:1$?

In an examination out of $480$ students,$85 \%$ of the girls and $70 \%$ of the boys passed. How many boys appeared in the examination if the total pass percentage was $75 \% ?$

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

$A$ mixture contains $80 \%$ acid and the rest water. The part of the mixture that should be removed and replaced by the same amount of water to make the ratio of acid and water $4:3$ is