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Comment by kjeetgill | Hacker News Reader

I've always counted in 5s, or really more like a 3+2 or 2+2+1. The garden party for me is keeping the number in my head so knowing the last digit is always 0 or 5 makes it easy. Then you just add the remainder at the end.

That's roughly how you count change too.

Ex: if I were to count 21 items my mental count would be 2,3 [5] 3,2 [10] 2,2,1 [15] 2,3 [20] and 1. [21]

Hope that makes sense!

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I used to be in vending.

For bills and coins, I count by object, not denomination. Then multiply total by denomination.

For counting large numbers of bills, I like creating stacks of 20. Then I count the number of stacks. After that I make stacks of 100 bills, and wrap them. In this way, I am never 75 bills deep, lose count and have to restart.

I know I have to count each stack of twenty twice, and ideally not three times, so I count 21 bills out, then if its 21 the second time, I take one off.

For piles of coins(and socks, et al), remove the most common/visible/largest type. For example, I would remove $1 coins into their own pile/bag, not bothering to count yet. Then as they become less obvious, I switch to $2 coins, then $0.25, then $0.05(since they are larger than $0.10 coins).

I had an electronic coin counter, but away from the office, that's how I sorted coins. If I wanted to count on site, it was a lot easier to count homogeneous bags. I could also weigh for a rough estimate.

> I know I have to count each stack of twenty twice, and ideally not three times, so I count 21 bills out, then if its 21 the second time, I take one off.

I'm not sure I understand this. Is it just so you don't have to hunt for an extra bill somewhere else? If the second count doesn't match the first count you need to count a third time anyways, right? It sounds like you're implying using a 21 stack initially reduces recounts.

It's weird, all right. Counting twenty would surely be just as convenient.

Very interesting — I'd like to try this. Do you have any sense of whether this is as reliable as counting by one, two or three? That is, if you were counting out something really important, would you do it this way? Was there much of a learning curve?

I think its advantage is reliability. I don't know if it does much for speed.

You can't make off by 1 or 2 errors because then you'd end up with a count like 23 or 27. You're counting by 5... the last digit needs to be 0 or 5! And you're not going to make an off by 10 error.

You can visually pick out 2s and 3s to make your 5 before you add them in.

In my experience, you can make off by 1 or 2 errors when you accidently include 1 or 2 items in different groups of 5 at the same time. You end up with 25 when you should have ended up with 23. It may also happen that you don't include 1 or 2 items in the groups, because you thought you'd already included them, while visually scanning the area. When that happens, you end up with 25 when you should have ended with 27.

I'm not kjeetgill, but I also group things visually in 5 when counting.

On your question, I feel less confident in my count, the more things I have to count. Since there will always be fewer groups of 5 than groups of 1, I always feel more confident counting in groups of 5 than of 1.

EDIT:

It's like divide and conquer. You divide the work by first making sure each group has only 5 items by glance counting (what kjeetgill means with 2 + 3), and then you count the groups, and add what didn't fit in any group.

Having the work divided like this makes it easier to verify that it was all done correctly. You'll end up feeling more confident about some groupings than others (because of the way the items are positioned) and you'll just want to recheck the ones you're not so confident about and readjust accordingly. Once you're confident in the groupings, you can recount the groups more easily than having to recount each individual thing.

For most sums, you'll end up adding less than 5 or 10 things at each step, which is easy.

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