$A$ person covers half of his journey at $30 \text{ km/h}$ and the remaining half at $20 \text{ km/h}$. The average speed for the whole journey is (in $\text{km/h}$)

Two trains start at the same time from Mumbai and Pune and proceed towards each other at the speeds of $60\, km/h$ and $40\, km/h$, respectively. When they meet, it is found that one train has travelled $20\, km$ more than the other. Find the distance between Mumbai and Pune (in $km$).

Paschim Express left Delhi for Mumbai at $14:30\, \text{hours}$ travelling at a speed of $60\, \text{km/h}$. August Kranti Express left Delhi for Mumbai on the same day at $16:30\, \text{hours}$ travelling at a speed of $80\, \text{km/h}$. How far away from Delhi will the two trains meet (stoppages excluded)? (in $\text{km}$)

Two guns were fired from the same place at an interval of $13 \text{ minutes}$,but a person in a train approaching the place hears the second shot $12 \text{ minutes } 30 \text{ seconds}$ after the first. Find the speed of the train,assuming that sound travels at $330 \text{ m/s}$ (in $\text{km/hr}$).

$A$ car covers four successive $7 \, km$ distances at speeds of $10 \, km/h$,$20 \, km/h$,$30 \, km/h$,and $60 \, km/h$ respectively. Its average speed over this total distance is (in $km/h$):

Two trains,$A$ and $B,$ start from stations $X$ and $Y$ towards $Y$ and $X$ respectively. After passing each other,they take $4\, \text{hours } 48\, \text{minutes}$ and $3\, \text{hours } 20\, \text{minutes}$ to reach $Y$ and $X$ respectively. If train $A$ is moving at $45\, \text{km/h},$ then the speed of train $B$ is (in $\text{km/h}$)