+4711 There are 16 benches in a park and 9 big bushes.
The benches are set out by 4x4, so a huge square and thee bushes are placed in the centre of every tiny (4) squares.
Also displayed as,
There are 4 spies in the park who are making secret phone calls, so they don't want be seen by each other!
How many different possibilities are there for each Spy to sit on a bench without being seen by each other?
(Can you use permutation to solve this?)
Please show workings so I can understand thanks!
PS:Even my brother found this hard!
+129899 I get the same answer as Alan....but with a slightly different explanation...
The first spy can sit in any of the first four "vertical" benches . The next spy has three vertical benches to choose from. The third spy has two and the last one has one. That's 4 x 3 x 2 x 1 = 4! ways = 24 ways. But, once seated, we can also arrange these vertical columns in 4! ways.....so....4! x 4! = 24 x 24 = 576.
+118687 Yes I think this is quite hard M.G.
It looks like a good puzzle. I will add it to our puzzles thread 
+33661 They must all sit in different rows and different columns.
I think this means there are 16 places for the first spy, 9 places left for the second spy, 4 places left for the third spy and just 1 left for the fourth spy. So I'm going with 16*9*4*1 = 576 possibilities.
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+129899 I get the same answer as Alan....but with a slightly different explanation...
The first spy can sit in any of the first four "vertical" benches . The next spy has three vertical benches to choose from. The third spy has two and the last one has one. That's 4 x 3 x 2 x 1 = 4! ways = 24 ways. But, once seated, we can also arrange these vertical columns in 4! ways.....so....4! x 4! = 24 x 24 = 576.
+118687 Okay I get the same answer too but my explanation is a little different again.
I'm going to put spy1 in row 1 that is 4 ways
spy2 i row 2 that is 3 ways
spy3 in row 3 that is 2 ways
spy 4 in row 4 that is 1 way so so far I have 4*3*2*1 = 4! Just like CPhill.
Now there are 4P4 or 4! permutations for the order that the spys can be chosen in.
So the number of ways is 4!*4! = 576
