MetaChat - Ask MeCha: Percentages

Divide 72 by 10 = 7.2 (10%)

Divide 72 by 100 = .72 (1%)

7.2 + .72 + .72 = 8.6 ~ 9 (~12%)

posted by AlexReynolds 15 February | 10:54

Yeah, rounding is the trick. There's a great section in Freakonomics about "street math".

posted by matildaben 15 February | 10:56

Damn, I was coming to post exactly what AlexReynolds did. yep, base everything around working from 10%

This method also makes it very easy to work out tips.

posted by gaspode 15 February | 10:57

First, is it evenly divisible? In your example, 9/72 = 1/8 = 12.5%. Easy enough. If it's not quite evenly divisible, but close, you can estimate the difference from there.

Second, if it's not evenly divisible, I start with a bench mark percentage that's easy to figure out. For example, 10%, 25%, or 50%. Then you can estimate the difference from there. To use your example, again, 10% of 72 is 7.2. 9 is a little over that, so add a couple of percentage points, and you end up very close to the accurate percentage of 12.5%.

posted by brainwidth 15 February | 10:58

I normally just do the division (i.e. 9/72 = .125 = 12.5%) in my head. If accuracy doesn't matter I just figure out 10% and 5% and guess from there (i.e. 10% = 7.2, 5% = 3.6, so 9 is approx 12-13%).

posted by pivo 15 February | 10:58

Hehe, or yeah, what everyone else beat me to the punch with.

posted by pivo 15 February | 11:00

Similarly, if you know that
1/2 is 50%
1/3 is 33%
1/4 is 25%
1/6 is 66%
1/8 is 12.5%
1/16 is 6.25%

Then you can usually get close by adding these up.

posted by Capn 15 February | 11:00

By the way, working out a 15% tip is super easy...

Say the bill is $235.77 (you big spender), calculate 10% by moving the decimal place up one, so $23.57, round up (because you're generous like that) to $24, then add half that again $12 for a total of $36.

posted by Capn 15 February | 11:02

I thought segmenting the problems would be the route to go. I'm working on some market-sizing problems for a possible case interview, and I've not had to do weird percentage stuff [13 million is what percentage of 280 million] in 6 years or so.

I have no trouble working with bases of ten, so tip calculation is easy. I'll refresh myself on some fraction/decimal relations and that will help too.

posted by sciurus 15 February | 11:05

I honestly don't know how I do percentages in my head. I just do. This is why my math grades where always so bad. I could get the answer, but didn't know how to "show my work."

I do know that I always tip 20% because then I only have to double the first number or two of the total.

posted by jrossi4r 15 February | 11:11

In the UK our VAT (sales tax) is 17.5%, and that's easily worked out by dividing the number by ten (10%) then halving the 10% (5%) and then halving that number to get 2.5% and adding them all together.

So if something costs £64 + VAT you add 6.4 + 3.2 + 1.6 to work out the VAT of £11.20.

posted by essexjan 15 February | 11:32

I should first point out that I'm crap at maths.

Whenever I get confused I resort to how I was taught percentages by a mad bitch of a nun.

Let's say you know the cost of something but like to know how much it would with an additional 27%. You write this down:

$83 = 100%
? = 127%

In other words "I know 83 dollars is one hundred percent but I don't know how much will it be as 127%"

You now multiply the diagonally opposed numbers and divide by the number left on it's own. In this case:

83 x 127 / 100

And if only wanted the amount of the increase then it'd be:

$83 = 100%
? = 27%

which leads to:

83 * 27 / 100

And of course it works the other way around too:

$83 = 100%
$1.34 = ?

which leads to:

1.34 * 100 / 83

Hardly the most efficent method, but very easy to remember and it's hard to get too confused. I still feel kind of dumb sharing this though - it seems a stupid way of doing things.

posted by dodgygeezer 15 February | 11:57

Yeah, like everyone else, if it's obviously divisible (like the first example), I just figure out it's 1/8 and that 1/8 is half of 25%, or 12.5%. Otherwise, I tend to use the essexjan method of adding 10%, 5%, and 2.5% until I have the number I want. My mother taught me this when I was seven or so, and it's one of the most helpful things I've ever learned.

Also, you are not generous if you tip 15%. Tip 20% to be real stand-up.

posted by dame 15 February | 12:01

Capn, I do tips the exact same way. Everyone else in Washington State multiplies the tax by 2 but since I like to choose whether I tip 15% or 20%, I use the "move decimal point" method and then add half (if 15%) or just multiply by 2 for 20%.

posted by matildaben 15 February | 12:05

WtF? Didn't you memorize your division tables in school?

And when can you ever not use a calculator? I carry one with me just in case I end up on a train leaving New York at 5...

That said, I'll do averages. 8 is what percent of 30? Well, three goes into 8 more than 2 times, but less than three. I happen to know that it's actually 2/3rds more than 2, so I'd say about 2 2/3%. Then deal with the decimals as necessary (becomes 26.667%, roughly). You can always check your math if you end up with a weird decimal (like a .4). 26 × 3 = 78, and then just iterate ( + .6 x 3 = 1.8 ) = 79.8, etc.

Or you can approach it from the multiplication angle, or "How many times does 8 go into 30?" "Between three and four but closer to four" then "ok, so between 1/3 and 1/4, but closer to 1/4 or 25%."

I've repeated a few people, but there you have my take on things.

And for calculating tips, I just memorized the times tables up to 15. 15 times the first 1 or 2 numbers and then round to the nearest cent. Unless you suck, in which case no tip for you. There, I said it, haters.

posted by Eideteker 15 February | 12:22

Excuse me, nearest DOLLAR. Fuck change.

posted by Eideteker 15 February | 12:24

15? I tip 15% just because the place is open!

posted by mullacc 15 February | 12:24

You 15% tippers should all be ashamed of yourselves. And know I won't go out to dinner with you. Because I hate make up stingy people's tips.

posted by dame 15 February | 12:30

I embrace the concept of the "Super Tip." That's when everyone in a group just kind of throws all their money at the bill and you realize you have too much and you say, "Does everyone really want $ back, or should we just Super Tip?"

posted by jrossi4r 15 February | 12:36

I'm sorry, but that's the way I was raised. Until I see it in writing that you must tip 20% (by law), I'll keep tipping whatever I feel like. Gratuity is gratuitous. (I can link to like 7 of these convos on the Blue). I tip a baseline of 15 cause that's what I was taught. I tip less for a poor server (not kitchen but server) and more for good service (like water glass never empty, etc.). Of course, sometimes I tip whatever I feel like, just to fuck with people. Was the service shitty? Am I just an asshole (accent on the just; we know I'm an asshole but are exploring other variables at this point)? Am I too poor to tip more? You don't know! Because a tip is a shitty means of communication, so I don't rely on it.

And if I'm with someone who calls me stingy for leaving ANYTHING extra (= gratuitous), I say: "Fine, YOU cover the tip," and leave nothing. OMG THE UNWRITTEN RULES OF SOCIETY BROKEN. Well, until they're written, I can't see 'em.

And if I ever find a restaurant that says: "No tips, please. We pay our staff an actual living wage." I will eat there all the time. And I will still tip for good service. Because it's a shitty job to have and good for you if you can do it well. Not good for you for taking a shitty job in the first place, but hey, you gotta eat.

(Would I be a good jonmc protege if I agreed with you on anything, dame? Just checking.)

posted by Eideteker 15 February | 12:43

You are a Good Person (tm), jrossi.

And Eide, I don't care how many words you spill, not tipping 20% makes you a Bad Person (tm). Frankly, people who try to justify being stingy are worse. A tip is part of how much it costs to eat at a restaurant. And claiming that because it's not written down you can do whatever you want is extra repulsive. I will never go out anywhere with you.

posted by dame 15 February | 12:46

The Capn is not a 15% tipper, this was presented as advice for figuring out the minimum acceptable tip.

posted by Capn 15 February | 12:46

Eideteker: Do you base your 15% on pre-tax or post-tax, pre-wine or post-wine?

posted by mullacc 15 February | 12:47

You are a Good Person (tm), jrossi.

Not really. Just an Ex-Waitress (tm).

posted by jrossi4r 15 February | 12:52

I tip 18% baseline, up to 22% if exceptional. Always pre-tax.

posted by gaspode 15 February | 12:59

Dame: It's settled then! ... Wait, we're in agreement!

mullacc: Pretax, Idon't-drink.

No, really, I usually tip random amounts because I'm lazy and hate change. So if it looks good on the credit card receipt and rounds to an even dollar amount, I'm done! I honestly don't know how much I tip most times. 27%? 12%? Who cares, I dine alone mostly, so I usually end up making it =$10 and call it a day. But the idea of an invisible standard of tipping (which used to be 15%, but that's the problem with invisible numbers; you can't prove they've changed because they're not written down).

My mother always tipped 15% unless she was pissed. That's how I learned. If you have a complaint, tell my mom she's been doing it wrong all these years. Stingy is a relative term, based on what you're taught. If I start tipping 20% (one FIFTH of the meal price; in other words five people have to pay for six to eat out) then next year people will call me cheap for not tipping 25%. Because it's a percentage, you don't have to inflate it. It adjusts for inflation automatically. That's the beauty of it.

I'm not calling the 20%+'s out there liars, but I'm just saying that ain't the way I heard it. (Actually, MeFi is the ONLY place I've heard of 20% tips. Maybe it has to do with affluence, of which my youth was absent.)

posted by Eideteker 15 February | 13:00

Sorry:

"But the idea of an invisible standard of tipping (which used to be 15%, but that's the problem with invisible numbers; you can't prove they've changed because they're not written down)..."

... infuriates me. It reeks of Miss Manners and false propriety. Prim and proper ("No elbows on the table." "Why?" "Because I said so." "Take off your hat indoors." "Why?" "Because I said so." "You pledge allegiance with your RIGHT hand." "Why? I'm left-handed." "Because I said so.") for the sake of being prin and proper without any reason or rationale. Most cultures don't have tipping, and I'm sorry but it's not my fault we let a particular industry in our economy erode to the point where it's exempt from minimum wage laws. If it's any consolation, I try to eat out as little as possible, because the thought of the whole thing makes me angry.

Unable to finish thoughts? Yeah, about that nap...

posted by Eideteker 15 February | 13:08

I don't think the poor thing is it. I gre up without much. That's why I give. It's the same way poor people always give more to panhandlers: we know how much it sucks to not have money. And I would do nearly anything to not wait tables.

Also, pre-tax? Also stingy. Geez, it's an extra dollar, if that.

posted by dame 15 February | 13:08

Really dame (pre-tax = stingy)? Because I didn't grow up with tipping, so when I moved here I tried really hard to learn about the proper etiquette and most people told me that you always tip pre-tax.

I don't really have an internal barometer for these things.

(and consequently stress a lot for things like getting my hair cut becuase I just don't know what to do)

posted by gaspode 15 February | 13:16

I've always tipped post-tax, too. Anyway wait-staff here know what the standard is?

I think tipping is a fascinating thing to discuss even though it has been done a million times. Anyway, dame's observation is one of the most interesting facets of tipping - some of the most consistent "good" tips I got as a valet were from people driving some of the shittiest cars. But I've witness plenty of exceptions to this trend.

Also, I've only been to Europe once (and only to Budapest) and I didn't think to tip any differently. I've since heard that tipping is much less common there, but I don't think I'll be able to change my ways when I go next.

posted by mullacc 15 February | 13:23

Indeed. That stress is unnecessary, gaspode. Here's what you do: Don't tip. And then if they say: "A-hem, it is customary to give a tip." you say, "Well then, thanks for the tip!"

But then, I cut my own hair, and into a style that is impossible to fuck up.

posted by Eideteker 15 February | 13:25

I've found that tipping the person that cuts your hair is one of the few places where tipping results in tangibly better service. Presuming you go to the same person each time.

But for many other services, the need to tipp is indeed ambigious and that causes me stress.

posted by mullacc 15 February | 13:31

The technical standard is 15-20% on the pre-tax total. But most people I know calculate with tax.

I tipped in Budapest, too, mullacc. (Beautiful city and I got in touch with my Hungarian roots.) Actually, I don't know that I've ever gone anywhere and not tipped.

But I will not tip the girls at the muffin store with the self-serve coffee. All they do is hand me a cup. Why the tip jar?

posted by jrossi4r 15 February | 13:41

I'm in line with gaspode, that 18% (post-tax) is my baseline. If somebody gets less than 18%, that means they provided unapologetically flawed service.

Eideteker, for what it's worth, I routinely tip over 20% (particularly on small checks), and could make an extremely long list of friends, family and associates who do so, as well.

Much of this rounding comes because I round the post-tip total so I can pay without getting change. If a bill is $16, I leave a $20. If it's $400, I'll make it an even $500.

And jrsossi, I love your name for the supertip. I despise bistromathics, and greatly prefer your way.

Of course the other solution to the supertip is to gamble for the check, loser pays the whole thing. In the long-run, it evens out nicely, and in the short run, it's fun.

posted by mosch 15 February | 13:43

or the asian gambling method: winner pays the whole thing.

posted by mosch 15 February | 13:44

Well, there is one situation in which I don't tip: at a place where they don't have table service (except Burritoville, because the guys who work there are THE BEST). That shit's just out of conrol. (On preview, I see you agree, jrossi.)

And podee, it just seems silly to me to tip pre-tax. It isn't very much money & I don't mind helping someone else out. So yeah, it's like haggling over a dollar. And these days, as poor as I may be, I always have a buck.

posted by dame 15 February | 13:46

also agreed re: not tipping to be handed a bagel.

The only time I've tipped at starbucks was when the people I was with all ordered absurdly complicated drinks, (so much so that I thought they had to be kidding). I tipped there as my way of saying "I don't think what they ordered should exist."

posted by mosch 15 February | 13:49

I've gotten so use to puting my change in tip jars (the coins, not the bills), that I'm actually annoyed when there isn't one there.

posted by mullacc 15 February | 13:55

I always tip Dick Cheney when we go on hunting trips. Safer that way.

posted by orthogonality 15 February | 19:56

15 February 2006