MJP & Mathematical Riddle, page-5

Guys... If it takes 10 days to produce 1 jet pack that does not mean that only 1 is getting produced at any point of time. There will be many in the production line and the reason it may take 10 days, is it may be because certain activities can only be done by a certaion person or group. Hence it moves in a production line. So whiel it may take 10 days, for a single jetpack to come off the prouction line, the next one may only get spat out 4 hrs later!