If two-third of $A$ is four-fifth of $B ,$ then $A : B =?$

Find the $4^{th}$ proportional to $4, 16$ and $7$.

On the entire Earth,the ratio between land and water is $1:2$,and in the Northern Hemisphere,this ratio is $2:3$. What will be the ratio of land to water in the Southern Hemisphere?

Find the compound ratio of $2:7$,$5:3$,and $4:7$.

$A$ and $B$ have their monthly incomes in the ratio $8: 5,$ while their monthly expenditures are in the ratio $5: 3.$ If they save ₹ $12,000$ and ₹ $10,000$ monthly respectively,then the difference in their monthly incomes is (in ₹): (in $,000$)

If an alloy contains copper and silver in the ratio $3:7$,then the percentage quantity of silver in the alloy is