In what proportion must tea worth $75$ paise per packet be mixed with tea worth ₹$5.50$ per packet so that the mixture may cost ₹$4.50$ per packet?

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 $,000$)

In what ratio must $25 \%$ hydrochloric acid be mixed with $60 \%$ hydrochloric acid to get a mixture of $40 \%$ hydrochloric acid?

$A$ person has a chemical costing $Rs. 25$ per $litre$. In what ratio should water be mixed in the chemical so that by selling the mixture at $Rs. 20$ per $litre$,he may get a profit of $25\%$?

Three glasses of capacity $2 \, L$,$5 \, L$,and $9 \, L$ contain mixtures of milk and water with milk concentrations of $90 \%$,$80 \%$,and $70 \%$ respectively. The contents of the three glasses are emptied into a large vessel. Find the ratio of milk to water in the resultant mixture.

$18 \text{ litre}$ of pure water was added to a vessel containing $80 \text{ litre}$ of pure milk. $49 \text{ litre}$ of the resultant mixture was then sold,and some more quantity of pure milk and pure water was added to the vessel in the respective ratio of $2:1$. If the resultant respective ratio of milk and water in the vessel was $4:1$,what was the quantity of pure milk added in the vessel? (in $\text{litre}$)