You have two hour glasses one measures 7 minutes and the other measures 4 minutes.
Using these two-hour glasses, you need to measure exactly 9 minutes.
In 2011, people playing Foldit, an online puzzle game about protein folding, resolved the structure of an enzyme that causes an Aids-like disease in monkeys. Researchers had been working on the problem for 13 years. The gamers solved it in three weeks.