Two trains of equal lengths take $10 \; s$ and $15 \; s$ respectively to cross a telegraph post. If the length of each train is $120 \; m$,in what time (in $s$) will they cross each other when travelling in opposite directions?

$A$ train $360 \; m$ long is running at a speed of $45 \; km/hr$. In what time (in $sec$) will it pass a bridge $140 \; m$ long?

Two trains running at the rate of $45 \; km/h$ and $36 \; km/h$ respectively,on parallel tracks in opposite directions,are observed to pass each other in $8 \; seconds$. When they are running in the same direction at the same rate as before,a person sitting in the faster train observes that he passes the other in $30 \; seconds$. Find the length of the trains (in $m$).

$A$ train $280 \; m$ long, running with a speed of $63 \; km/hr$, will pass a tree in (in $sec$):

Two goods trains,each $500 \; m$ long,are running in opposite directions on parallel tracks. Their speeds are $45 \; km/hr$ and $30 \; km/hr$ respectively. Find the time (in $seconds$) taken by the slower train to pass the driver of the faster one.

Two trains are moving in opposite directions at $60 \; km/hr$ and $90 \; km/hr$ respectively. Their lengths are $1.1 \; km$ and $0.9 \; km$ respectively. The time taken by the slower train to cross the faster train in seconds is