Question

SSC Test Questions

A car covers 4 successive 3km stretches at speed of 10kmph, 20kmph, 30kmph & 60kmph resp. Its average speed is ?

Answer 1

$S_{av}= \frac{total\ distance}{total\ time}\\\\ S_{av}= \frac{3 \times 4}{ \frac{3}{10}+\frac{3}{20}+\frac{3}{30}+\frac{3}{60} }\\\\ S_{av}= \frac{4}{ \frac{1}{10}+\frac{1}{20}+\frac{1}{30}+\frac{1}{60} }\\\\S_{av}= \frac{4}{ \frac{6+3+2+1}{60}}= \frac{4 \times 60}{12}=20\ kmph$

Answer 2

Answer:

The average speed of car is 20kmph

Step-by-step explanation:

We know,

Average speed  = ( Total distance ) / ( Total Time )

Firstly, We calculate the total time taken by car :

Time = Distance /  Speed

Time taken when travelling at a speed of 10 kmph:

Speed = 10 km/hr

Distance = 3 km

Time = 3 / 10 hr

Time taken when travelling at a speed of 20 kmph:

Speed = 20 km/hr

Distance = 3 km

Time = 3 / 20 hr

Time taken when travelling at a speed of 30 kmph:

Speed = 30 km/hr

Distance = 3 km

Time = 3 / 30 = 1 / 10 hr

Time taken when travelling at a speed of 60 kmph:

Speed = 60 km/hr

Distance = 3 km

Time = 3 / 60 = 1 / 20 hr

Total time:

T = 3/10 + 3/20 + 1/10 + 1/20

= ( 6 + 3 + 2 + 1 ) / 20

= 12 / 20

= 3 / 5 hour

Total distance:

D = 3 * 4 = 12 km

Average speed = ( Total distance ) / ( Total time )

Substituting the values,

Speed = 12 / ( 3 / 5 )

Speed =  ( 12 * 5 ) / 3

= 60 / 3

=20 kmph

Hence,

The average speed of car is 20kmph