Question

8. A boy leaves his house at 9.30 a.m. for his
school. The school is 2 km away and classes start at
10.00 a.m. If he walks at a speed of 3 km/h for the
first kilometre, at what speed should he walk the
second kilometre to reach just in time?​

Answer 1

SPEED OF BOY

Given, distance of school from his house,d = 2km

Since, the starting time is 9:30 am, where he need to reach school at 10:00 am, So time taken, t = 30 minutes.

Also, The boy travels first kilometre at the speed of 3km/h, Time taken in doing so:

⇒ Distance = Speed × Time

⇒ 1 = 3 × t

⇒ t = 1/3 × 60 [∵ 1 hour = 60 minute]

⇒ t = 20 minutes

Since, He has spent 20 minutes of 30 minutes, So he would need to get to school within 10 minutes.

Now, Time taken, t = 10 minutes or 1/6 hour

Distance remaining, d = 1 km [∵ He travelled the first kilometre]

We know,

⇒ Speed = Distance / Time

⇒ Speed = 1/(1/6)

⇒ Speed = 6 km/h

Hence, The speed of boy should be 6 km/h in order to reach just in time.

Some Information :-

• Average Speed :-

Average distance is distance travelled per unit time throughout the whole journey. We can find Average speed by using the given formula:

⇒ Average Speed = Total Distance Travelled / Total Time Taken