Egg timers

Here is a variation on one of Richard Wiseman's Friday puzzles.

Puzzle

For dinner you decide to make a soft boiled ostrich egg. Problem is, an ostrich egg needs to boil for exactly seven minutes. After searching through your kitchen drawers, you find two hour-glass-style egg timers: one for three minutes, the other for five minutes. Is it possible to time exactly seven minutes using these timers? Is it possible to do so without any preparation?

See also

• Die Hard III
• Nine minute fuse
• Sharing water

References

Richard Wiseman's blog