I'm buying a home gym set-up for my son (really!) and I want to know the fewest number of weight plates I need to buy to be able to go up in 5kg increments to 170kg. The bar weighs 20kg and the weights are available in 25kg, 20kg, 15kg, 10kg, 5kg and 2.5kg. It is cheaper per kilogram to buy bigger plates (£25 2.5kg, £40 5kg, £70 10kg, £90 15kg, £120 20kg and £145 25kg). Weights come in pairs and when a pair is used one plate must go on either side.
The pairs need to be split evenly because of the risk of unbalancing due to moments (levers/physics) and hence the risk of injury. My son wouldn't want to have to refer to a chart for every weight increment (although feel free to solve it if you want, it is a standard 7' Olympic bar).
Can I do better than just buying a pair of each?
(Note that I do not know, but feel that there is a better answer.)