Given: The ratio of the speed of the bike, van and lorry = 3 ∶ 7 ∶ 5 Distance covers by lorry = 360 km Time taken by lorry to cover = 12 hours Concept used: Speed = Distance/Time Average = (Total sum)/(Total terms) Calculations: Let the speed of the bike, van and lorry be 3x, 7x and 5x respectively Speed of lorry = 360/12 = 30 km/h ⇒5x=30 ⇒x=6 Speed of bike =3x=3×6=18 Speed of van =7x=7×6=42 Average speed of bike and van =(18+42)/2=30 km/h ∴ Average speed of bike and van is 30 km/h