Question

A aeroplane flies along the four sides of a square at the speeds of 20km/hr, 40km/hr, 60km/hr and 80km/hr. Find the average speed of the car around the field? ( approximately) Select one: a. 35km/hr b. 38km/hr c. 40km/hr d. 32km/hr

Answer 1

Answer :

384km/hr

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Answer 2

Given:

Speed of aeroplane is 20km/hrs., 40km/hrs., 60km/hrs. and 80km/hrs. respectively.

Let us assume that the side of the square = LCM (20,40,60,80)= 240 km.

time taken across the first side = distance/speed = 240/20

=12 hrs.

times taken across the other three sides = 240/40 = 6 hrs.

times taken across the other three sides 240/60 = 4 hrs.  

times taken across the other three sides 240/80 = 3 hrs.

total distance = 240 × 4 = 960 km.

total time = (12+6+4+3) = 25 hours.

average speed =960/25

average speed = 38.4 km/hrs.

It approximately 38 km/hrs.

The correct option is "b"

Hence the  average speed is 38 km/hrs.