0

If I want to multiply with multiple percentage increases, I convert it to decimal and then calculate.

Example: 1 * 1.4 * 1.2 = 1.68

Now, I came across someone on reddit who calculates it the following way:

1 + 40% + 20%

Which started an argument with different people, saying the second way is false, taking google as an example. If you put this into google, it says the result is 1.6. If you put it into wolfram alpha, it adds brackets and calculates it correctly.

The redditor argues it's a computational issue. And I'm starting to wonder if he is right or if google is right.

Would

1 + 40% + 20% = 1 + 60% = 1.6

or

= 1.68

Common sense tells me, the redditor is right, but then I think "google is big and they know their shit". I'm asking this because I'm curious, not because I want to prove someone wrong. And sorry if this lacks the proper formatting, I don't have a background in maths.

Punishbear
  • 1
  • I would simply say $x%=\frac{x}{100}$, so that $1+40%+20%=1+40/100+20/100=1.6$ but it's all a matter of notation. – Jean Daviau Aug 17 '23 at 14:50
  • 5
    The simple answer -- "$20%$ *of what*?" – PrincessEev Aug 17 '23 at 14:50
  • It's a matter of how the question is interpreted. It's not clear from the wording "adding percentages to a number" as to which of the two answers is intended. It would have to be made more clear in the original problem. If you were, say, talking about interest being applied to some invested amount, then you would have $168%$ of your principle amount. If you were talking about, say, eating pizzas, it could be different. Say I had a whole pizza, then $40%$ of Casey's Pizza and $20%$ of Darren's, then I would have eaten $1.60$ pizzas. More context is needed to say one or the other is right. – Theo Bendit Aug 17 '23 at 14:56
  • It's just number crunching in the context of Path of Exile, an ARPG where you have multipliers to damage. The game arrives correctly at 1.68, it's a question of peoples notation on how to get there. – Punishbear Aug 17 '23 at 14:58
  • If only math notation was standardised to that degree (as it is not). For some people, $40%$ just means $0.4$ and $20%$ just means $0.2$ so $1+40%+20%=1+0.4+0.2=1.6$ (Try out $2+40%+20%$, what does Google say?). For other people, "$+40%$" is a unary postfix operation of adding $40%$ (basically multiplication by $1.4$). You cannot tell what the result of evaluating an expression is if you don't understand (or if it is ambiguous) what the expression means in the first place! I believe everyone there (Wolfram Alpha, Google, Reddit user) is correct with respect to their meaning. –  Aug 17 '23 at 15:05
  • @StinkingBishop your 2+40%+20% example is very interesting. Google "mixes" the meaning of expressions, as it arrives at 3. Thank you for your comment. Avoiding ambiguousness is super important for this. – Punishbear Aug 17 '23 at 15:15
  • Yep. What is worse, Google does $(2+40%)+20%$ very well ($3.36$) so, for Google, $2+40%+20%\ne(2+40%)+20%$. Curiouser and curiouser. –  Aug 17 '23 at 15:18

0 Answers0