$A$ man goes from a place $A$ to $B$ at a speed of $12 \, km/h$ and returns from $B$ to $A$ at a speed of $18 \, km/h$. The average speed for the whole journey is? (in $km/h$)

$A$ train starts from Delhi on Sunday at $9 \, am$ with a speed of $25 \, km/h$. Another train starts from the same place on the same day at $3 \, pm$ with a speed of $40 \, km/h$ in the same direction. Find at what distance from Delhi both trains will meet? (in $km$)

$A$ train leaves the station at $5 \, am$ at $60 \, km/h$. Another train leaves the same station at $6.30 \, am$ at $75 \, km/h$ and travels in the same direction as the first train. At what time and at what distance from the station will they meet?

The distance of the sun from the earth is $143,400,000 \text{ km}$. Light travels from the sun to the earth in $7 \text{ minutes}$ and $58 \text{ seconds}$. The velocity of light per second is (in $\times 10^5 \text{ km/sec}$):

$A$ thief is spotted by a policeman from a distance of $400\, m$. When the policeman starts the chase,the thief also starts running. Assuming the speed of the thief is $5\, km/h$ and that of the policeman is $9\, km/h$,how far will the thief have run before he is overtaken by the policeman? (in $m$)

Ramesh sees a train passing over a $1 \, km$ long bridge. The length of the train is half that of the bridge. If the train passes the bridge in $2 \, minutes$,the speed of the train is (in $km/h$)