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Small little disclaimer, it is my first time posting a question, so any feedbacks on what I should improve on when asking questions would also be appreciated.

On to the question proper:

I am a teacher and one of the next topic I am preparing for is the topic of rate. I am searching for real-life examples of rate, and one of the examples that hit me is whether the pricings at supermarkets (or anywhere that have pricings for that matter) can be considered rates.

I do know that rate is the ratio between two quantities. Like in the example of speed, $30$ $km/h$ means that for every hour I travel, I move $30$ $km$. In the case of pricing, lets say the price tag of a chocolate bar is $\$2$, it actually means $\$2$ per bar of chocolate, which is why I think it can be considered a rate. However, supermarkets do not put the price tag as $\$2$/bar or $\$2$/item, just simply $\$2$. So my confusion now stems from whether it is because it is actually not a rate, and I have gotten the concepts of rate wrong, or it is a rate, just that the supermarkets choose not to put the price as a rate for cost/efficiency purpose.

Things I have considered:

  1. It is possible it is not a rate because neither price nor item is a SI unit, as compared to $km/h$. But then what do we make of the fuel consumption of a car $(km/l)$?
  2. Further to point 1, maybe fuel consumption is a bad example because l can be converted to $cm^3$. But then what do we make of heart rate (beats per minute)?

To summarise my question,

  1. Can pricing be considered a rate?
  2. If it is not considered a rate, why? And what makes it different from the examples in the considerations?
meta_warrior
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Njh332
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    Some stores give the price per ounce on their tags for some canned good. But yes - prices can be considered a rate, especially so when talking per measurement (ounce, kilogram, ...) – Sean Roberson Jul 15 '21 at 08:04
  • https://www.mathsisfun.com/definitions/rate.html – John Douma Jul 15 '21 at 08:06
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    Yes it can be considered a continuous rate, particularly price per Kg. This might not be linear (directly proportional) in reality: the more (Kg) you buy of something the more % discount you get. But if we pretend this "% discount" doesn't exist, then yes, Kg is proportional to price, so there is a linear/proportional rate there. – Adam Rubinson Jul 15 '21 at 08:08
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    Oh right! I was too fixated on off-the-shelf price tags, which simply just puts the prices like $2 (at least in my local supermarkets) I forgot that there exists items like meat and such which are sold by weight. That was rather big blunder on my part. Thanks to all for your patience and detailed answers! – Njh332 Jul 15 '21 at 08:24

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