There are two lengths of rope. Each one can burn in exactly one hour. They are not the same length or width as each other. They also are not of uniform width (they might, for example, be wider in middle than on the end), thus burning half of the rope is not necessarily 1/2 hour. By burning the ropes, how do you measure exactly 45 minutes worth of time?
As ever, please free to say if you think you have solved it and how long it took, but please no solutions. Answer on Monday!
Oh, and if you are struggling to find something to do on this fine day, here is my science stunts video again!