Question

A boy leaves his house at 9:30 a.m. for his school. The school is 2 km away and classes starts at 10:00 a.m. If he walks at a speed of 3 km/hr for the first kilometre at what speed should he walk the second kilometre to reach just in time?

Answer 1

Answer:

6 km/hr

Explanation:

He has 30 minutes to reach the school.

When he starts walking at 3km/hr, he will take 60/3 = 20 minutes to walk first kilometer. Now he has 10 minutes to cover same distace (i.e. 1 km) thus he will have to walk at double the speed he was walking i.e. 6 km/hr.

Answer 2

Question

$\bigstar$ A boy leaves his house at 9:30 a.m. for his school. The school is 2 km away and classes starts at 10:00 a.m. If he walks at a speed of 3 km/hr for the first kilometre at what speed should he walk the second kilometre to reach just in time ?

Answer

Starting time , t1 = 9:30 am

Total distance , d = 2 km

Final time , t2 = 10:00 am

Speed for 1st kilometer , s1 = 3 km/h

Speed for 2nd kilometer , s2 = ? km/h

Case 1 : -

For whole distance

Distance, D = 2 km

Time, T = 30 min = 1/2 h

Case 2 : -

For first one kilo meter

Distance , d1 = 1 km

Speed , s1 = 3 km/h

Time = Distance/ speed

=> Time, t1 = 1/3 h

Case 3 : -

For remaining one kilo meter

Distance = 1 km

Time = T - t1 = 1/2 - 1/3= 1/6 h

Speed = Distance / Time

=> Speed = 1/(1/6) = 6 km/h

So , he should walk with the speed of 6 km/h for the remaining one kilo meter.