It is a way of raising prices without the actual price of the product going up. You just get less for the same amount of money. The manufacturer is hoping you won't notice. Most people just grab the item and put it in the shopping trolley without looking at it especially if they buy the product often.
950 ml when you change the oil filter, but just 900 ml if you dont change the oil filter
950 ml/ litre = 950 ml / 1000 ml = 950/1000 = 19/20
1L = 1000 ml so 950 ml/1000 ml = 0.95 as a fraction
1000mL
exactly 950
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7500mL = 7.5 L There are 1000mL in a L, so you simply divide your mL by 1000 to get L.