Forget those old maths problems about how long six men will take to mow an acre of grass. Here's a question that's only too relevant to the real world.
If 58 per cent of offenders discharged from British prisons are re-convicted within two years, and the prison population currently stands at 73,000, how well is our penal system performing on a scale of one to 10?
The answer, of course, is not nearly well enough.
And when the question is narrowed down to young men, the picture is bleaker still, with more than three-quarters risking their new-found freedom by getting straight back into crime.
Tell all that to the people in question, however, and the statistics would probably go clean over their heads. Why? Because a disproportionately high number of prisoners - around 75 per cent of them - have such poor numeracy skills that few employers would consider giving them work.
And therein lies the crux of the problem. For long-term employment, along with a stable relationship and somewhere to live, is known to be a major factor in deterring ex-offenders from returning to crime.
As few as one in 10 people leaving prison has any immediate prospect of a job. Which is why improving levels of numeracy and literacy among serving prisoners, and those who have been released or who are serving sentences in the community, is now seen as key to bringing down crime levels.
At Onley Prison, near Rugby, the head of education, Cymbre Baseley, offers inmates aged between 18 and 80 the opportunity to study maths at any level, from simple sums to an Open University degree. But much of the emphasis is on basic skills, the aim being to bring as many prisoners as possible up to Level 2, or GCSE equivalent, before release.
"Nowadays there isn't a job that doesn't need maths, English and IT," she says. "Having a maths GCSE doesn't guarantee you a job, but not having it can stop you getting one."
For basic numeracy skills, tutors follow the Skills For Life programme, and value the flexibility that it offers.
"Adults have got spikey profiles," says Baseley. "They might have understood fractions at school but they can't do long division to save their life. So ... we just do the division bit, which enables them to get a qualification."
At Onley, numeracy and literacy are taught side-by-side in joint workshops.
With a specialist in both subjects to hand, students can easily switch - or be switched - from one to another.
"Some people like one and some the other," says Baseley, "and what they tend to like and what they need to improve on are generally the opposite.
But that's part of our teachers' jobs - to say, 'Yes, I know you like English, but I'm not having you sitting here writing stories when you can't add up'."
Baseley finds that reluctant mathematicians can be eased into the subject one small hurdle at a time. "It's a case of persuading them that they're not thick, and finding a way that works for them. If you have to go back to the old abacus, then you can do."
At the same time, students with good maths skills but poor literacy can often be persuaded to harness their ability with logic and sequencing to overcome their difficulties with English.
"We get a more intensive feel for the basic skills side here," says Baseley, "which is why a lot of the Government's basic skills targets are being met by prisons."
She stresses, however, that basic skills alone are not enough. Which is why her students are encouraged to take supplementary courses in money management, which is taught at Level 2.
"It homes in on things that they'll really need when they leave here - things like budgeting, bank statements and wages. These are key factors if they are to avoid being conned, and they enjoy it because they can see the use of it."
Similarly, higher-level students at Onley are encouraged to get a qualification in basic book-keeping, since many see self-employment as the way forward. "A straight maths qualification isn't going to get you a job, but book-keeping will," says Baseley. "What they need is linked qualifications."
Tony Uden, senior research fellow at the National Institute of Adult Continuing Education and author of Learning is not a crime, believes that making maths relevant is especially important when teaching offenders.
"There has been a tendency in the past to regard financial literacy as being a step beyond numbers," he says. "That's like making people learn to read Janet And John before you allow them to read the Sporting Post."
In fact, teachers should not shy away from using examples such as betting, or even the price of cigarettes, as a way into numeracy, he says. "You're trying to connect with people's lives where they are, not where you want them to be."
In the case of short-term prisoners - those serving less than a year - the problems are intensified, and there is sometimes a danger that education will be forced off the agenda altogether by more pressing needs such as sorting out drugs or mental health problems.
Critics have pointed out that too many petty but persistent young offenders have, in the past, been released back into the community only to find themselves in debt, with nowhere to live and no relationship, yet without any form of supervision, and equipped for little other than crime.
According to a recent survey, says Uden, only 6 per cent of prisoners continued with education after release, which is why he welcomes recent moves to introduce supervision of ex-offenders in the community and continuity of learning opportunities.
Typical of the organisations offering such support and training is the Manchester Re-education Resettlement Centre. A charity, funded from a variety of sources, MERC offers free numeracy and literacy classes to around 250 students each week - people who are unable to access mainstream education and who find their way to the centre via the probation service or through drug and alcohol agencies.
Here, the emphasis tends to be less on job-seeking and more on simply coping with everyday life. "It's often a case of confidence-building," says Jane Owen, a co-ordinator at MERC. "People in prison, or living in hostels or supported housing, easily become institutionalised, and it must be so much more difficult to look after yourself if you are not numerate."
While it might in the past have been easier to hide poor number skills than illiteracy, Owen points out that changes in the way benefit is paid - into bank accounts rather than over a post office counter - mean that it will become increasingly difficult for people to get by without some knowledge of money management.
But although learning how to do sums has undoubted utility outside prison, Steve Connor, a basic skills tutor at MERC for the past five years, says it can also have less tangible and somewhat unexpected benefits.
"Funnily enough, once people actually start doing numeracy here, they really enjoy it," he says. "Very few things in life work out, but maths actually does. Two plus two always equals four, and sometimes people just like the idea of sitting down and doing sums. And if they are actually enjoying their maths, when they do go into a shop and see 10 per cent off something, it doesn't seem quite as scary as before. And that's quite a confidence booster."