I look at grocery-store lines like betting on horses. The goal is to pick the winning horse -- the line that moves the fastest. And when you get stuck behind someone who has neither her coupons nor checkbook ready, you picked a bad horse.
Now common sense would dictate that you head to the Express Line (12 items or less) even if there are more people there than in the traditional checkout lanes. You feel like the average transaction should be shorter and you'll be on your way faster. But if you do the math, according to blogger Dy/dan, any checkout lane with more people is likely to be the longer line, even if they have fewer items.
It's a fascinating mathematical breakdown of a very mundane thing -- the time it will take you to complete your grocery purchase. The key appears to be to look at people and not items in the cart:
When you add one person to the line, you're adding 48 extra seconds to the line length (that's "tender time" added to "other time") without even considering the items in her cart. Meanwhile, an extra item only costs you an extra 2.8 seconds. Therefore, you'd rather add 17 more items to the line than one extra person.Each person is potentially 48 seconds of additional wait time, and that doesn't even account for the person who can't figure out how to scan their credit card or needs a price check on bananas.