In a race of 900 meters, Shreya beats Rahul by 15 seconds or 225 meters. Find the time in which Shreya finished the race?

Option 2 : 45 seconds

GIVEN:

Length of race = 900 meters

Shreya beats Rahul = 15 seconds or 225 meters.

CONCEPT:

Relative speed.

CALCULATION:

As Rahul lost by 15 seconds or 225 meters, that means he would have covered 225 meters in 15 seconds only.

So, Speed of Rahul = 225/15 = 15 m/s

So,

⇒ Time in which Rahul covers 900 meters = 900/15 = 60 seconds

Hence,

⇒ Time in which Shreya finished the race = 60 – 15 = 45 seconds

Alternate Method

Shreya travels 225 m in 15 seconds

Her speed = 225/15 = 15 m/s

Then, the distance she travels to finish the race = time taken to travel (900 - 225 m)

 She finishes the race in = 675/15 = 45 s 

∴ The time taken by Shreya to finish the race is 45 seconds.