This maths question for 10-year-olds has grown ups stumped

One dad was scratching his head at a maths problem his son got at school. The puzzle, aimed at Year 5 students in Derbyshire, UK, has drawn a blank from even pro problem solvers.

The dad, 43, who got A-levels in maths in economics, said: “My son’s grandma had spent a while helping him with his homework and most of it was straightforward but this one question left her stumped. I then spent an hour or so trying to work it out but found it impossible. I even sent it to a friend who got a 1st class degree in economics and they were baffled by it as well. A couple of friends are maths teachers too so I’ve sent it to them but so far I’ve heard nothing back. I really do think it is impossible and it is certainly not something a ten-year-old can answer. It just does not make sense.” Do have a crack at it after the cut...