Two cities

The car goes from city A to city B at an average speed of 70 km/h and back at an average speed of 50 km/h. If it goes to B and back at an average speed of 60 km/h, the whole ride will take 8 minutes less. What is the distance between cities A and B?

Correct answer:

s =  140 km

Step-by-step explanation:

v1=70 km/h v2=50 km/h v3=60 km/h t=8 min h=8:60  h=0.13333 h  s = v1 a s = v2 b 2 s = v3 (a+bt)  2 s = v3 a+v3 bv3 t  2 s=v3 (s/v1)+v3 (s/v2)v3 t 2 s=60 (s/70)+60 (s/50)60 0.13333333333333  20s=2800  s=202800=140=140 km  s=140   Verifying Solution:   a=s/v1=140/70=2 h b=s/v2=140/50=514=2.8 h c=a+bt=2+2.80.1333=3144.6667 h



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