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Comments on If a changes to b, then doesn't a + d = b? Why a(1 + d) = b?

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If a changes to b, then doesn't a + d = b? Why a(1 + d) = b? [closed]

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Closed as unclear by Peter Taylor‭ on Mar 23, 2023 at 13:58

This question cannot be answered in its current form, because critical information is missing.

This question was closed; new answers can no longer be added. Users with the reopen privilege may vote to reopen this question if it has been improved or closed incorrectly.

My 9 year old does not grok DanielWainfleet's answer. How can we intuit why percent change divides the difference by the original number, NOT the new number?

If a changes to b then $\color{red}{a(1+d)=b}$ so $d=(b/a)−1=(b−a)/a$.

Why $\color{red}{a(1+d)=b}$? Why can't this be $\color{limegreen}{a+d=b}$? Isn't it more straightforward to symbolize change as $\color{limegreen}{d}$, rather than $\color{red}{ad}$ ?

If I have 2 apples, and buy 3 more, then my new amount of apples $\color{seagreen}{= 2 + 3 = 5}$. NOT $\color{firebrick}{2(1 + 3) = 10}$.

Math SE deleted a similar question.

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Define "d". (3 comments)
Define "d".
Olin Lathrop‭ wrote about 1 year ago

This question makes no sense since you don't define what your expectations are of "d". If A changes to B, then there certainly is a value D where A + D = B. You seem to have some expectations about D, but since you didn't state them, your premise in the question is false. -1 since this should have been obvious.

Chgg Clou‭ wrote about 1 year ago

I don't need to define "d", because DanielWainfleet did so in his answer on StackExchange.

Olin Lathrop‭ wrote about 1 year ago · edited about 1 year ago

Yes you do. When you ask here, information pertinent to the question needs to be here. Links can be used for background information, but any question here needs to be understandable and answerable without following links. This question was correctly closed as unclear since you didn't define your terms.