If you want to get through the supermarket checkout more quickly, avoid the 'express' queue and stand behind someone with a full trolley.
That's the surprising advice from Dan Meyer of Desmos, a US organisation that promotes maths, technology and data.
His research has shown that while items take around three seconds each to be scanned, another 41 seconds is accounted for by greeting the cashier, paying, putting away your purse and clearing out of the way.
All that means that standing behind one person with 100 items will mean an average wait of less than six minutes, compared with almost seven minutes waiting behind four people with 20 items each.
And it's not just the number of items that makes a difference, it's the number of different items: six bottles of the same wine will take less long to process than six different varieties. Meanwhile, anything that needs to be weighed, such as fruit and vegetable, will also take longer.
You should also look at the people in the queue - somebody clearly in a hurry is going to get through the checkout a lot more quickly than somebody who looks in the mood for a chat or who is clutching a handful of coupons. Children may slow down the progress of shoppers in front of you - another adult will probably help pack.
And, he tells the New York Times, "This may seem sexist, but I prefer female cashiers. In my experience they seem to be the most expedient at register transactions and processing."
And you can make the cashier's job easier by placing your items on the conveyor belt in such a way that the bar code can be clearly seen.
Earlier this summer, Which? sent out a group of undercover shoppers and found that Tesco had the quickest checkouts, at an average of two minutes 43 seconds. In Morrisons it was two minutes 47 seconds, and in Sainsbury's three minutes 10 seconds.
Shoppers in Asda had the longest average wait at four minutes 52 seconds.
But it's worth remembering that you don't always pick the longest queue - however much it may feel that way. As David Andrews points out in 'Why Does the Other Line Always Move Faster?', we tend to compare our own queue with the ones either side - which means that we only have a one-in-three chance of being the fastest.