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Time Speed Distance 1/2

7.  What is the average speed if a person travels from A to B and then B to C at the speeds of 10 km/hr and 20 km/hr, respectively for equal intervals of time?
a. 15 kmph
b. 13.33 kmph
c. 12 kmph
d. 11.11 kmph


8.  What is the average speed if a person travels from A to B and back at the speeds of 10 km/hr and 20 km/hr, respectively?
a. 15 kmph
b. 13.33 kmph
c. 12 kmph
d. 11.11 kmph


9.  A car covers four successive three km stretches at speeds of 10 km/hr, 20 km/hr, 30 km/hr and 60 km/hr respectively. Its average speed over this distance :
a. 10 km/hr
b. 20 km/hr
c. 30 km/hr
d. 25 km/hr


10.  A train covers a distance in 50 minutes. If it runs at a speed of 48 km per hour on an average, the speed at which the train must run to reduce the time of journey to 40 minutes will be :
a. 50 km/hr
b. 55 km/hr
c. 60 km/hr
d. 70 km/hr


11.  A man goes uphill with an average speed of 35 km/hr and comes down with an average speed of 45 km/hr. The distance travelled in both the cases being the same, the average speed for the entire journey is :
a. $38\displaystyle\frac{3}{8}$ km/hr
b. $39\displaystyle\frac{3}{8}$ km/hr
c. 40 km/hr
d. None of these


12.  P and Q are two stations. A train goes from P to Q at 64 km/hr and returns to P at a slower speed. If its average speed for the whole journey is 56 km/hr, at what speed did it return?
a. 48 km/hr
b. 49.77 km/hr
c. 52 km/hr
d. 47 km/hr