In a row of girls, if Savitha who is tenth from the left and Anita who is ninth from the right interchange their places, Savitha becomes fifteenth from the left. How many girls are there in the row?

How many $7$s are there in the following series which are immediately preceded by $6$ but not immediately followed by $4$?
$7, 4, 2, 7, 8, 4, 3, 6, 7, 5, 3, 5, 7, 8, 4, 3, 7, 6, 7, 2, 4, 0, 6, 7, 4, 3$

Abhishek ranks thirteenth in a class of thirty-one students. What is his rank from the last (in $19^{th}$)?

The letters $L, M, N, O, P, Q, R, S$ and $T$ in their order are substituted by nine integers $1$ to $9$ but not necessarily in that order. $4$ is assigned to $P$. The difference between $P$ and $T$ is $5$. The difference between $N$ and $T$ is $3$. What is the integer assigned to $N$?

In a queue of children,Kashish is fifth from the left and Mona is sixth from the right. When they interchange their places among themselves,Kashish becomes thirteenth from the left. Now what will be Mona's position from the right (in $^{th}$)?

Manisha ranked sixteenth from the top and twenty-ninth from the bottom among those who passed an examination. Six boys did not participate in the competition and five failed in it. How many boys were there in the class?