Expert: Chanda Walker - 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
First, usually groups that large need to tip at 15% BUT if you want to tip at 13% so be it.  I'll give you a tip for both tips.  Also, for groups that large, often they include the tip already in the bill.  Be sure you don't double tip.

13%:

First thing to do is take the total and move the decimal place over one place making it smaller.

Example:
$243. 17  -> $24.31  I'd round that DOWN to $24. (Be sure to round DOWN!)

Now, divide that by 3.  $24/3 = $8

Add them back together and you get a tip of $32.

The exact tip at 13% would be: $31.6

Now just add that to the total and since you can do the math on the receipt, you don't have to do that in your head.

15% is easier :)
Start the same way by moving the decimal over.  Then cut that number in half and add it back to the first number so.

$24 + $12 = $36

This time if you rounded down, add a little back in.  If you rounded up, take a little off.

I'd add push that up to $36.50 since we rounded down.

The exact tip would have been $36.48.

Also, you can ask slip a note to the waiter saying please write what a 13% tip would be.  Do this before hand on a little sticky note and attach it to your credit card on the back side.  They will let you know the appropriate tip.