Question

A man starts from his home at 10:00am walks with a speed of 10 kilo meter per hour on a straight road up-to market 20km away stays at the market till 2:00 pm and return home by an auto with speed of 20km per hour average speed over this interval

Answer 1

Acc. To me,

Answer is 40/3 km/h

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s1(speed of going)=10km/h

s2(speed of returning)=20km/h

d=20km

Avg speed =total distance/total time

Total d=d+d(for going and returning)

total time=t1+t2(for going and returning)

You don't know time so find out by

s=d/t

For t1(going)

s=s1,d=d,t=t1 so

t1=d/s1---------1

Here for t2(returning)

s=s2,d=d,t=t2

t2=d/s2------------2

Put it and find

avg S=2d/t1+t2

avg S=2*s1*s2/s1+s2------3

Put s1 and s2 in equation 3 and find

Avg S=40/3 km/h

I hope it help