Hitesh is $40$ years old and Ronnie is $60$ years old. How many years ago was the ratio of their ages $3:5$?

If $P: Q = 8: 15$,$Q: R = 5: 8$,and $R: S = 4: 5$,then $P: S$ is equal to

$10 \ yr$ before,the ratio of ages of $A$ and $B$ was $13: 17$. After $17 \ yr$ from now,the ratio of their ages will be $10: 11$. The present age of $B$ is (in $yr$):

The sum of two numbers is equal to $25$ and their difference is $20$. The ratio of the two numbers is

There is $1000 \, \text{litres}$ of milk in a pot. $100 \, \text{litres}$ of milk is taken out and the same amount of water is poured into it. Again, $200 \, \text{litres}$ of the mixture is taken out and the same amount of water is poured into it, and finally, $400 \, \text{litres}$ of the mixture is taken out and the same amount of water is poured into it. What is the amount of milk in the resulting mixture?

The ratio of the present ages of $R$ and $S$ is $11:17$. $11$ years ago,the ratio of their ages was $11:20$. What is $R$'s present age (in years)?