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

In a college,$150$ students of $MBA$ are enrolled. The ratio of boys to girls is $7:8$. There are three disciplines in the college: Marketing,$HR$,and Finance. In the Marketing discipline,there are $50\%$ girls of their total number and the boys are $40\%$ of their total number. In the $HR$ discipline,girls are $30\%$ of their total number while boys are $30\%$ of their total number. The Finance discipline has girls $20\%$ of their total number and the boys are $30\%$ of their total number. $7$ boys and $9$ girls are in $HR$ and Marketing both. $6$ boys and $7$ girls are in $HR$ and Finance both. $5$ boys and $8$ girls are in Marketing and Finance both. $2$ boys and $3$ girls are enrolled in all the three disciplines. By what percent is the number of boys in the Marketing discipline more than the number of girls in the $HR$ discipline?

The difference between the ages of Meena and Seema is $3 \ yr$ and the ratio between their ages is $7: 8$. What is the sum of their ages (in $yr$)?

If $A: B = 2: 3$,$B: C = 4: 5$,and $C: D = 6: 7$,then $A: B: C: D$ is

Two numbers are in the ratio $2:3$. If $2$ is subtracted from the first and $2$ is added to the second,the ratio becomes $1:2$. The sum of the numbers is:

Sachin is younger than Rahul by $4$ years. If their ages are in the respective ratio of $7:9$,how old (in years) is Sachin?