Question

A car travels first 30 km at a uniform speed of 20km/hr and next 30 km at a uniform speed of 40km/hr. What is the average speed?

Answer 1

solution:  av speed= 2s/1/v1+1/v2         s= distance (this is applicable only when distance same)
                             2x30=60
                             1/20+1/40=3/40             steps are solved separately
                   now divide them both
                              we get ,
                                         av speed= 60x40/3
                                                        = 800km/h
     if time intervals are same then av speed can be found out by taking the average of speeds