Question

a car travels 30km at a uniform speed of 40km/h and next 30km at a uniform speed of 20km/h. find its avg speed.

Answer 1

Formula is D1*T1+D2*T2/D1+D2
(30*40/60 +30*20/60)/30 + 30 =0.5 km per minute.

Answer 2

Average speed = Total distance / Total time
= x / (t₁ + t₂)
= x / [x/(2v₁) + x/(2v₂] ………[∵ Time = Distance / Speed]
= 2v₁v₂ / (v₁ + v₂)
= (2 × 40 kmph × 20 kmph) / (40 kmph + 20 kmph)
= 26.67 kmph

Average speed of car is 46.67 kmph