Complex price deals are turning a trip to the shops into a math exam.
There are so many different sizes and prices that spotting the cheapest deal in the supermarket aisles could have even Sherlock Holmes or Columbo in a flummox.
In a study, one in five struggled to find the best value in a range of everyday products
At a time when one in two families are looking to reduce their food bill, the study found that ten percent of shoppers result to taking a calculator with them to get their groceries.
It started to get tricky when people had to calculate prices per gram, kilo or litre.
Ralph Risk, marketing chief at Lightspeed Research, the company responsible for the survey, said: 'It seems people get very confused when metrics are mixed - from pints to packets, grams to kilos, jars to loose fruit and veg.'
But the confusion is good news for the supermarkets as shoppers are habitually paying more.