Reply To: Sunday Puzzle thread
Given how you describe the puzzle, I am giving two answers:
1) which is in the spirit intended:
A and B cross — takes 2 min with running total 2
A returns — 1 min, running total 3
C and D cross — 8 min, running total 11
B returns — 2 min, running total 13
A and B cross — 2 min, running total 15
2) As it WASN’t stated that they had to cross at night (!) then they just wait for the morning. They cross in the light so the torch isn’t needed and they can go in any paired order they like! From above, C+D = 8 + A+B =2 gives a crossing of 10 mins with no torch in daylight.
I do like the second solution. Speaks to a lateral way of thinking that might appeal to our sponsors at GCHQ. Mind you I think they would also like the first answer!!Harry