In a mixture of milk and water of volume $30$ $L$,the ratio of milk and water is $8:7$. How much water should be added to the mixture to make the ratio $4:5$? (in $L$)

In what proportion must a grocer mix sugar at ₹ $12$ per $kg$ and ₹ $7$ per $kg$ so as to make a mixture worth ₹ $8$ per $kg$?

The ratio in which tea costing $Rs. 192$ per $kg$ is to be mixed with tea costing $Rs. 150$ per $kg$ so that the mixed tea,when sold for $Rs. 194.40$ per $kg$,gives a profit of $20\%$,is:

How much water must be added to a vessel which contains $80$ litres of milk at a cost price of ₹ $3.5/litre$ so that the cost of the milk reduces to ₹ $2/litre$? (in litres)

How many $kg$ of sugar costing ₹ $5.50$ per $kg$ must be mixed with $60 \ kg$ of sugar costing ₹ $4.80$ per $kg$ so that the mixture is worth ₹ $5.25$ per $kg$?

$49 \ kg$ of blended tea contains Assam and Darjeeling tea in the ratio $5:2$. The quantity of Darjeeling tea to be added to the mixture to make the ratio of Assam to Darjeeling tea $2:1$ is..........$kg$.