A car travels for 15km in a city at a certain speed. Outside city is travels 72km at twice it's former speed. If the total travelling time is 1hr 8mins, find the average speed in the city.
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Answer:
45 km/h.
Step-by-step explanation:
Average speed in the city V = 15/t where t ( minutes) is the time traveling in the city.
Outside the city it travelled at a speed of 2V.
Time the car travels when out of the city = 68-t minutes
Average speed outside the city = 72/(68-t) = 2V.
So we have the 2 equations
V = 15/t
2V = 72/(68-t)
From the first equation :
t = 15/V, so substituting this into the second equation:
2V = 72/(68 - 15/V)
2V( 68 - 15/V) = 72
136V - 30 = 72
V = 102/136
= 0.75 km / minute
= 0.75* 60
= 45 km/h.
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