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This may sound like a dumb question, but I was comparing the calcium content in almond milk (45% of daily value per serving) vs. cow milk (30% per serving) and ran into this problem. It appears almond milk has 1.5 times the amount of calcium per serving than cow milk (correct me if I'm interpreting the percentages wrong). Does that mean that there is 50% more calcium in almond milk or just 15% more? The serving size is the same for both milks.

It seems like it would be 50% more since it's 1.5x as much calcium, but since we're dealing with percentages already do you just subtract 30 from 45?

I guess my general question is, when comparing two percentages, do you simply subtract one from the other or do you divide one from the other to get the ratio?

5AMWE5T
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    Don't forget to compare what volume a "serving" is for each item. – Zev Chonoles Aug 13 '16 at 20:17
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    When you talk about percentages, you have to keep in mind percentages of what. Both are done, but both mean different things. In your example, it is $50%$ more calcium total in the almond milk (per serving), whereas it is $15%$ more of your daily serving value (per serving). – JMoravitz Aug 13 '16 at 20:20
  • I forgot to add that the serving size was the same for both, so I was comparing the same volume. – 5AMWE5T Aug 13 '16 at 20:21
  • Funny enough, both 15% and 50% are valid answers, depending on what you actually mean. – naslundx Aug 13 '16 at 20:26
  • The General answer is: never compare percentages. You are comparing percentages of the "Daily value", let's say it is 100ug (micrograms), so one serving of almond milk gives 45ug and one serving of cow milk gives 30ug, now it's easier to compare values: one serving of almond milk gives 15ug more of calcium that is 50% more than cow milk and 15% more of the Daily value. – N74 Aug 13 '16 at 20:29
  • And do not forget that cow milk contains about $33.3%$ less calcium than almond milk. – quid Aug 13 '16 at 20:34
  • https://books.google.com.br/books?id=RLuJmE5y8pYC&pg=PA9&lpg=PA9&dq=non+newtonian+calculus+galileo&source=bl&ots=mky_zuatrQ&sig=91CzIB8nTDFljk_Py7MqWZmzywg&hl=en&sa=X&ved=0ahUKEwj3vsDeirXOAhXKjZAKHUvKBlgQ6AEITzAG#v=onepage&q=non%20newtonian%20calculus%20galileo&f=false – Michael Hoppe Aug 13 '16 at 23:24

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Almond milk contains $50\%$ more calcium than cow milk. And, almond milk also contributes $50\%$ more towards your daily need than cow milk does, as $0.45 = 1.5 \times 0.3$.

However, almond milk contributes $15$ percentage points more towards your daily need than cow milk does.

That is, there is a specific terminology to address the ambiguity you observe.

quid
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