Wikipedia:Reference desk/Archives/Mathematics/2015 March 4

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March 4

1.2% + 250 %

Is 1.2 percent plus 250 percent 2.512 percent or 4.2 percent? — Preceding unsigned comment added by 199.119.235.240 (talk) 03:12, 4 March 2015 (UTC)

That depends on the base:

A) 1.2% (of 100) + 250% (of 100) = 251.2%.

B) 1.2% (of 100) + 250% (of 1.2%) = 4.2%.

Note that neither of my answers matches your first answer.StuRat (talk) 03:22, 4 March 2015 (UTC)

I don't see how to get your choices. Without a context, 1.2% + 250 % = (1.2 + 250)% = 251.2% = 251.2/100 = 2.512. Something else may be implied in a given context, especially if it doesn't literally say "1.2% + 250 %" but just something which could naively be thought to mean that. PrimeHunter (talk) 03:26, 4 March 2015 (UTC)

An example of the second case would be "The US Prime Rate was at 1.2% at the start of the year, but increased by 250% by the end of the year". StuRat (talk) 03:31, 4 March 2015 (UTC)

Right. I haven't seen notation like 1.2% + 250% for that but maybe it's used by some. PrimeHunter (talk) 04:10, 4 March 2015 (UTC)

I've never seen use "base" used to mean anything about percentages, except from Stu. Likewise, if that's what OP really means, then the usage by one is confirmed :) SemanticMantis (talk) 17:11, 4 March 2015 (UTC)

Stu is using "base" to mean "the thing you're talking about a percentage of". Unfortunately there actually isn't any common short expression for this, that I've come across. You won't find the word "base" in the Wikipedia article on percentage, or the MathWorld one either (here). Stu's comment is correct but might be more understandably expressed as "that depends on what you mean".

If a percentage increases from 1.2% to 4.2%, careful writers will often describe the increase as either a 250% increase (where 250 = 100 × (4.2/1.2 − 1)) or an increase of 3 percentage points (where 3 =  4.2 − 1.2). --70.49.169.244 (talk) 19:46, 4 March 2015 (UTC)

Right, I was just commenting on non-standard notation/terminology, and how we have at least one example right here in the thread. 20:25, 4 March 2015 (UTC)

Based on Wikipedia:Reference desk/Science#risk of cancer from oral sex, the poster did indeed mean starting with 1.2% and increasing by 250%, and 1.2% + 250% was indeed the poster's own formulation. PrimeHunter (talk) 01:36, 5 March 2015 (UTC)

I believe my usage is similar to that described in base rate. If nobody else has a better term for it, I'll stick with "base". StuRat (talk) 04:18, 5 March 2015 (UTC)

The term "base" for "that which a percentage of is taken" looks very familiar to me, and a quick Google search suggests its usage in this context is quite common (see e.g. a Khan Academy video). -- Meni Rosenfeld (talk) 16:34, 5 March 2015 (UTC)

Careful with your googling, there. To establish that a usage is really common, you also need to compare it against competing usages. --70.49.169.244 (talk) 17:43, 5 March 2015 (UTC)

If anyone is still reading, I never said it was wrong, just nonstandard. I guess I could be mistaken, but I've been learning math for over 30 years, and teaching it for over 15, so I suspected that I would be aware of it if it were truly common and conventional (in the USA). SemanticMantis (talk) 20:51, 10 March 2015 (UTC)