Semaphore

I am standing behind five pupils who are signalling a five-digit number to someone on the opposite side of the playground. What number is actually being signalled?

Problem

 

Image
Semaphore



I am standing behind five pupils who are signalling a five-digit number to someone on the opposite side of the playground.

From where I am standing the number looks like 23456.

What number is actually being signalled?

 

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.