Question

He sinhagad express left pune at noon sharp. two hours later, the deccan queen started from pune in the same direction. the deccan queen overtook the sinhagad express at 8 p.m. find the average speed of the two trains over this journey if the sum of their average speeds is 70 km/h.

Answer 1

Singhabad express takes time till 8 pm= 12 to 8 pm= 8 hr.
similarily deccan takes to overtake singhbad=2 to 8 pm=6 hr.
so the speed are in the ratio 3:4 hence it will be 30 and 40 km/hr respectively. since the sum is 70.
so average speed=total distance covered by both train/ total time
=(240+240)/(8+6)=34.28 km/hr. ans.

Answer 2

The average speed of the two train over this journey is 34.28 km/hr.

Given:

Deccan queen started from pune two hours late

Deccan queen overtook the singhagad express at 8:pm

Sum of average speed is 70 km/h

Answer:

Singhabad express took time till 8 pm = 12 hours

We know that 12 to 8 hours’ time = 8 hours

Similarly, Deccan queen started after 2 hours

That means, 2 to 8 pm = 6 hours

So, the speed ratio = 6/8 =3/4

The two train’s speeds are 30 and 40 km/hr respectively.

$Average \ speed = \frac {Distance \ covered \ by \ both \ trains}{Total \ time}$

$=\frac { (30\times 8+40\times 6) }{ (8+6) }$

$=\frac { (240+240) }{ 14 }$

$Average \ speed =34.28 \ km/hr$