A car covers the first half of the distance between two stations at a speed of 30 kmph and the others half at 60 kmph. Then its average speed is

Average speed= Total dis tan cecovered  Total timetaken =S2+S2t1+t2Where S=Total distancet1=S2V1t2=S2V2∴ Average Speed =S2+S2S2V1+S2V2=SS21V1+1V2=2V1V2V1+V2=2×30×6030+60=2×180090                                 =40kmph