Four friends need to cross a bridge.
They start on the same side of the bridge.
A maximum of two people can cross at any time.
It is night and they have just one lamp.
People that cross the bridge must carry the lamp to see the way.
A pair must walk together at the rate of the slower person:
What if we change how long it takes each person to cross?
There are two optimal strategies for solving this type of problem:
Strategy 1 solves the original problem in 17 minutes
Strategy 2 solves the original problem in 21 minutes
Experiment with different speeds and work out when to use Strategy 1 and when to use Strategy 2.
Is there a way of determining which strategy will be best?
Can you find sets of speeds for which both strategies give the same crossing time?
Printable NRICH Roadshow resource