Especially when you consider that most supermarket labels will also include the "price per unit weight" or "price per unit volume" on the shelf with a smaller font, it becomes trivially easy to compare which bottle of soap is going to get you the most for your money. Or maybe you neglect to do this (simply opting for the container that looks the most appealing rather than optimizing for the amount of liquid per dollar you'll receive) and as a result you have to suffer the catastrophic consequences of spending $9 per month on dish soap when you could have spent $7.20 instead.
The funny thing is that some of the asked are all arithmetic are constructed in such a way that you will get a "wrong" answer if you treat them as practical financial questions as opposed to purely arithmetic ones. For example, one of the sample questions in the article is "If a litre of cola costs $3.15, how much will you pay for a third of a litre?" This seems to be asking you to take $3.15 and divide it by three, but as a practical matter, it would be folly for me to take the price of a 20 oz soda bottle and then assume that I could calculate the cost of a 12 oz can simply by multiplying by 0.6. This question isn't a test of practical or financial literacy; it's purely arithmetic.
The funny thing is that some of the asked are all arithmetic are constructed in such a way that you will get a "wrong" answer if you treat them as practical financial questions as opposed to purely arithmetic ones. For example, one of the sample questions in the article is "If a litre of cola costs $3.15, how much will you pay for a third of a litre?" This seems to be asking you to take $3.15 and divide it by three, but as a practical matter, it would be folly for me to take the price of a 20 oz soda bottle and then assume that I could calculate the cost of a 12 oz can simply by multiplying by 0.6. This question isn't a test of practical or financial literacy; it's purely arithmetic.