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'Semaphore Signals' printed from https://nrich.maths.org/
Many of you sent in solutions to the first
part of this question, correctly saying that the message reads
"hello".
Yanqing who goes to Devonport High School for
Girls wrote to say:
I think there are 7+6+5+4+3+2+1=28 ways altogether:
There are 8 possible positions for a flag but you can't put
both flags in the same position, so when one of the flags is in
position 1, there are 7 positions where you can put the second
flag; when one of the flags is in position 2, because we have
already counted "one flag in 1 and the other in 2", we have 6 new
positions; when one of the flags are in position 3, we have 5 new
positions; ... and so on.
When we get to: one of the flags is in position 8, all of the
positions have already been counted, so we have:
7+6+5+4+3+2+1.
Well explained, Yanqing. Eva adds:
The 2 other combinations of directions are (NW, SE) and (N,
NE).