It is the classic "gotcha" question that should be the first thing all politicians learn the answer to before going anywhere near a television studio or a radio station: "How much is a pint of milk?".
That rule would perhaps apply even more if you are the farming minister attempting to deal with a potential protest by dairy farmers, over the price of milk.
Unfortunately Conservative Jim Paice was tripped up on BBC Radio 4's Farming Today programme on Tuesday morning.
Dairy farmers have said they may disrupt the Olympics unless a recent price increase is not reversed, warning it could push many of them out of business.
Paice said that while the price cuts announced last week were a "massive burden" for farmers he did not support "physical protest".
"If they want to come to London and exrepss their views then I entirely understand that and support it," he said. "If there are calls for more militant activity I will condemn it."
"Where do you buy your milk from Mr Paice?" asked presenter Anna Hill.
"We buy our milk either form a local supermarket which is one that has an aligned chain or from the corner shop in the village," Paice replied.
Hill added: "And do you know how much you pay for it?"
Paice replied: "No because my wife buys most of it, but I have checked with her where it comes from."
Maybe Mrs Paice should be in-line for a job in the next reshuffle.
Mary Creagh MP, Labour’s shadow environment secretary, said Paice was "completely out of touch with reality".
"Farmers and consumers will be shocked that he doesn’t know the price of milk when people are struggling to pay for their weekly shop and there’s a crisis in the dairy industry," she said.
“At the dairy summit tomorrow, Jim Paice will call for farmers to get a decent price for their milk - the trouble is, he is so incompetent he hasn’t a clue what it should be."
However National Farmers Union director of policy Martin Haworth was a bit more sympathetic.
"Not knowing the exact price of a pint of milk is very common," he said. "Our own research shows that most people don’t know the price but most would be willing to pay more, provided farmer’s get a fair price.”