Expert: Lynn Houston - 3/15/2009

Question
Hi there,
This isnt homework help, but I didnt see math anywhere else in this site, so I hope this is ok.
I organized a lunch for my boss/our team this week & am bad/slow @calculating tips. Strategies/ how 2 prepare?
There will be about 15 people total, I guess tip should be about 13% so the team doesn't get mad. I cant do math quickly in my head esp for such big numbers and don't want to appear inept. What are some strategies I can use to prepare for the next few days so I don't have to looks like a ditz in front of my boss? He has an MBA in finance and marketing so he is good at math.
Thanks much!

Answer
If you're in the US, the tip should be anywhere from 15-20%.  To figure 15%, first, round the bill, then take 10% (which is really easy) and add half of that to it.  For example a bill of 28.43.  Round to $28.  10% is 2.80, half of that is 1.40, so a 15% tip on $28 is 4.20.  If you want to do 20%, that is really simple, just double the bill and move the decimal.  Let's use 28.43 again.  Round to 28.  2 times 28 is 56, so the tip would be $5.60.  Another way, if your local take is around 8-9%, just double the tax amount.  To make it easier, round the tax amount to the nearest dime.  If the tax is 3.36, round to $3.40, double that to get $6.80.

If you're REALLY bad at math, just make a cheat sheet.  Go in $5 increments and just make a list of what the tip would be (whatever percentage you want) for each amount.  If you're going to have 15 ppl, you can probably start with $150 and go up to $250 in $5 increments.  That will be about 20 entries.  Either pick whichever number is closest to the bill total, or pick the entries on either side and pick a tip that is in-between the two.

Example:  Using the table below, which is %15, if the total bill is $163.  Either round and give $24.75 for the tip or pick something between 24 and 24.75

150 = 22.50
155 = 23.25
160 = 24.00
165 = 24.75

Hope this helps.