Did you ever have lunch/dinner with a group of friends and found that the chipped-in cash wasn't enough to pay the bill (including tax and tips)? I did, quite many times before. That's because some people only pay for what they see in the menu:
"$4.95 for the dish and $1.95 for the drink, alright here's $7, should be more than enough"
$4.95+$1.95 = $6.90, wow, 10 cents more!
Do you know that that you need to pay TAX & TIPS in this country?
In case you don't know (I'd be amazed), sales tax in the Los Angeles county is 8.25% and you should pay at least 10% tips to your server for any kind of restaurant (unless s/he did an exceptionally poor job, like spilling a bowl of soup on you). That's
1.0825 x 1.1 = 1.19075 or 1.2 for practical purpose
So, you should multiply what you see on the menu by 1.2 to find out how much you need to pay. If it's $6.90, you should actually pay $8.28. Always pay at or more than this amount. Bring quarters if you want to pay $8.50 instead of $9.00.
Bad at math?
You say you're bad at math and don't know how to multiply 1.2 in your head? Come on, just divide the menu amount by 5 and add it to the menu amount, that's it. One division and one addition, you can do it right?
But I can't remember the prices of my dish and drink
Then just try to remember the price when you order them. If you really forget, ask the waiter to give you the menu again. Some of my friends like to divide the bill amount by the total number of people and that's what you've to pay. This is just not fair. Some people order drinks and some people order water. Some people eat salad and some people prefer filet mignon. The differences in prices can be pretty big most of the times.
Come on guys! Isn't that so embarrassing to ask each person how much s/he pays when there's not enough money? (O__O )
P.S. By the way, I think that it's nonsense to pay tips according to certain % of the bill amount. Read about it here.