Tipping

Many of my friends struggle with the math needed to calculate the tip when we're out to dinner. My rule of thumb is that I tip 20% on average and adjust up and down from there. How do I determine 20%? Well, 10% is easy to figure out: you just move the decimal point one space to the left in the number you're looking at. Ten percent of $12.34 is $1.23. Pretty easy, huh? So then 20% is twice that. Twenty percent of $12.34 would be 2 x $1.23, or $2.46. So if your dinner bill was $12.34 and you wanted to leave a 20% tip, you would leave $12.34 + $2.46, which is $14.80 (don't forget to carry the 1...).