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

fred rosenberger
lowercase baba
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Joined: Oct 02, 2003
Posts: 11411
    
  16

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?


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Jayesh A Lalwani
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Joined: Jan 17, 2008
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  28

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
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Joined: Mar 28, 2012
Posts: 859

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

Joined: Aug 22, 2010
Posts: 3610
    
  60

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
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Joined: Jan 10, 2002
Posts: 61426
    
  67

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.


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Martin Vajsar
Sheriff

Joined: Aug 22, 2010
Posts: 3610
    
  60

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
Bartender

Joined: Jan 17, 2008
Posts: 2402
    
  28

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
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Joined: Mar 12, 2011
Posts: 808
It's the Law of Lines. You see, waiting, like matter, can neither be created nor destroyed. ;)
Ulf Dittmer
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Joined: Mar 22, 2005
Posts: 42278
    
  64
Martin Vajsar wrote:I never witnessed two trains in my direction before the opposite arrives.



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Bert Bates
author
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Joined: Oct 14, 2002
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    5
I really like Dan Meyer:

Dan Meyer

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

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Jesper de Jong
Java Cowboy
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Joined: Aug 16, 2005
Posts: 14269
    
  21

If you'd be in New York you'd be on the slow line...


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dennis deems
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Joined: Mar 12, 2011
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

Joined: Aug 06, 2012
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
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Joined: Sep 21, 2006
Posts: 152

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

Joined: Aug 11, 2007
Posts: 4659
    
    5

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.

vijay jamadade
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Joined: May 12, 2008
Posts: 241
this case you can have your wife on other line and you can take whichever is faster.


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( Nothing is Impossible.)
Kathleen Angeles
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Joined: Aug 06, 2012
Posts: 123

vijay jamadade wrote:this case you can have your wife on other line and you can take whichever is faster.


Doubles your chances!

Mr. Bean can use Teddy (his teddy bear).

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