Arthur D. answered • 09/17/16

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d=r*t

total distance=rate*total time

40=r*1 (35+25=60 min=1 hour)

r=40 kph answer

another solution more difficult..

20=r*(35/60)

20=r*(25/60)

20=r*(7/12)

20*(12/7)=r

r=34 2/7 kph

20=r*(5/12)

20*(12/5)=r

r=48 kph

now find the harmonic mean...

2*(34 2/7)*(48)/[(34 2/7)+(48)]=40 again after doing the arithmetic