At a showroom the average price of the scooters on display is ₹72,000 and the average price of the motorcycles is ₹96,000. There are three times as many scooters as motorcycles. What is the average price of all the vehicles on display?

Take 1 motorcycle and 3 scooters, which matches 'three times as many' whatever the actual numbers are. The four vehicles cost $3\times 72,000+96,000=216,000+96,000=$ ₹312,000, so the average is 312000/4 = ₹78,000. ₹84,000 is the plain midpoint of 72,000 and 96,000, which would be right only if the two kinds were equal in number; scooters outnumber motorcycles three to one, so the average must sit much nearer the scooter price. ₹90,000 attaches the counts the wrong way round, with three motorcycles to one scooter. ₹80,000 splits the ₹24,000 gap into three and adds one part, weighting by the number of KINDS rather than the number of vehicles.