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Aptitude Day 269


Problems on Time and Distance:

1. A person travels from P to Q at a speed of 50 km/hr and returns by increasing his speed by 20%. What’s his average speed for both the trips?

Solution:
                  120% of 50 = 120/100*[50] = 60 km/hr.

                  Average speed = 2*50*60/[50+60] 
                                          = 6000/110 
                                          = 54.55 km/hr.

2. A car travels the 1st one-third of a certain distance with a speed of 20 km/hr, the 2nd one-third with a speed of 10 km/hr, and the last one-third distance with a speed of 30 km/hr. The average speed of the car of the whole journey.

Solution:
                  Let the whole distance and speed be x and y respectively.
                  (x/3)/20 + (x/3)/10 + (x/3)/30 = x/y

                  By solving the above equation, we get
                  y = 180/11 
                     = 16(4/11) km/hr.



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