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# Why am I always in the slow line at the grocery store

fred rosenberger
lowercase baba
Bartender
Posts: 12198
35
So I realized something the other day.

You know how you go to the store, and it always seems like the 'other' line is moving faster than the one you are in? I think that is actually going to be true most of the time.

Clearly only one line can be the fastest. If there are two total lines, I have a 50-50 shot of being in the faster one.

However, if there are three, I only have a 33% chance of being in the fastest. And the odds of me being in the fastest line go down the more lines they have open.

Am I just slow to realize this? Has the rest of the world known this for years? Or am I onto something new here?

Jayesh A Lalwani
Rancher
Posts: 2756
32
I think the problem is that you are likely to notice the speed of your line when the line moves slow. In the instances that your line moves at an average speed, you probably won't realize it.

William P O'Sullivan
Ranch Hand
Posts: 859
• 1
I studied statistics as a second major, and the "bank teller" problem is classic (Wrote solution in SPSS! lol)

If you feel that you are always in the slowest line, then check what's in their carts.
Is there a bagger, or does the teller have to stop ringing/scanning and do the bagging also?
Do people have their wallets ready, credit/debit card, or a ton of coupons and bags of change? ;)

There are a lot of factors and always the outcome for efficiency should be 1 line, n tellers, not n lines, n tellers.

WP

Martin Vajsar
Sheriff
Posts: 3752
62
• 1
I've made similar observation in subway: sometimes there are two trains in the opposite direction before the train in my direction arrives.I never witnessed two trains in my direction before the opposite arrives. The inevitable conclusion is that the opposite direction has always shorter intervals. I believe this stems from some symmetry violation in the quantum world, which also causes the matter to be more abundant than antimatter in the universe, and immediate speedups of the lane I've just left in a traffic jam.

Or it is the observational bias. Hard to say.

Bear Bibeault
Author and ninkuma
Marshal
Posts: 65225
95
I always end up behind the person paying with pennies. Or with a check that they don't even start to make out until after the total is rung up. Or is arguing about expired coupons. Or wants their items rung up as three separate orders.

Martin Vajsar
Sheriff
Posts: 3752
62
Bear Bibeault wrote:I always end up behind the person paying with pennies....

I've once had my shopping processed at a cash register which froze in the middle and had to be rebooted. Only last few items (not the entire shoping) had to be processed again. Took some five minutes to get the damn thing up and running again. Didn't know MS is into the cash register business too

Now, beat that!

Jayesh A Lalwani
Rancher
Posts: 2756
32
This happens while driving too. Seems like when there is traffic, all lanes except yours are moving. When you change lanes, your lane stops moving again

dennis deems
Ranch Hand
Posts: 808
It's the Law of Lines. You see, waiting, like matter, can neither be created nor destroyed. ;)

Ulf Dittmer
Rancher
Posts: 42968
73
• 1
Martin Vajsar wrote:I never witnessed two trains in my direction before the opposite arrives.

Bert Bates
author
Sheriff
Posts: 8900
5
I really like Dan Meyer:

Dan Meyer

He did a pretty interesting study, with his high school students, of this very thing

Jesper de Jong
Java Cowboy
Saloon Keeper
Posts: 15485
43
If you'd be in New York you'd be on the slow line...

dennis deems
Ranch Hand
Posts: 808
Bert Bates wrote:I really like Dan Meyer:

Dan Meyer

He did a pretty interesting study, with his high school students, of this very thing

Thanks for introducing me to this blog! I really like it!

Kathleen Angeles
Ranch Hand
Posts: 123
mr. bean solved this probability problem.

he sneakingly pulled an item from the customer ahead and dropped that item, forcing the guy ahead to bend or reach down to get it. and thereby making an opening or chance for him to overtake, forcefully if needed. do until ahead==0.

Bill Clar
Ranch Hand
Posts: 163
I've noticed that a lane with a full cart doesn't always equal a slow line. People see a conveyor belt full of goodies and immediately move to the next lane.

Cashiers and baggers can make short work of a full cart. It's the coupons, checkbooks (haven't they outlawed personal checks yet?), and debit card n00bs that slow down the process.

Pat Farrell
Rancher
Posts: 4678
7
Airline ticket counters, car rental firms, and banks moved to one line feeding many workers decades ago. Its a trivial queueing theory example. I have yet to see any grocery stores with one line for many checkouts. They usually don't have the space. A person with a shopping cart takes more space than a person in a bank, or ticket line.

Ranch Hand
Posts: 243
1
this case you can have your wife on other line and you can take whichever is faster.

Kathleen Angeles
Ranch Hand
Posts: 123
vijay jamadade wrote:this case you can have your wife on other line and you can take whichever is faster.