Question

two trains start from the same station at 11pm. in opposite directions at speed of 72 km/h and 63 km/h respectively. at what time thsy will be 810 km apart?​

Answer 1

Let after x hours, the train will be 810 km apart.

Distance travelled by 1st train in x hours 63x km

Distance travelled by 2nd train in x hours= 72x km

$according \: to \: question$

$63x + 72x = 810$

$135x = 810$

$x = 810 \div 135$

$x = 6$

As the train started at 11p.m, we need to calculate 11p.m also

$11 \: hour + 6 = 17 \: hours$

So after 6 hours that is at 5.am. the train will be 810 km apart.

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Answer 2

Answer:

$\LARGE{ \underline{\underline{ \pink{ \bf{Required \: answer:}}}}}$

Consider the following question:

$Time = \frac{relaive \: Distanc }{relaive \: velocity}$

$= \frac{(810km)}{(72 \: kmph + 63 \: kmph}$

$= 6hours$

They’ll be 810 kmfrom start.6hr

They’ll be 810 kmfrom start.6hrIn other words, they’ll be 810km apart at 05:00PM

Hence, this is the required answer.

$\boxed{\sf\red{6Hours}}$