Question

One-fourth of certain journey is covered at the rate of 25 km/h, one-third at the rate of 30 km/h and the rest at 50 km/h. Find the average speed for the whole journey.
A.600/53km/h
B.1200/53 km/h
C.1800/53 km/h
D.1600/53 km/h

Answer 1

Answer:

         

Step-by-step explanation:

Let total distance be =12x

1/4 th journey=1/4 of 12x= 3x ,    time=3x/25

1/3 journey = 1/3 of 12x= 4x,       time = 4x/30=2x/15

rest journey= 12x-(3x+4x)=5x  , time =5x/50= x/10

total time=3x/25+2x/15+x/10=53x/150

Now average speed=total distance/total time=12x * 150/53x

=1800/53 km/h