Bob has sent us one solution:
6 4 9
5 7 8 3
2 1
George used algebra to tackle the
problem:
Call the numbers in the different dots a, b, ..., i, so the W looks
like
a e i
b d f h
c g
Then a+b+c=13, c+d+e=13, e+f+g=13, and g+h+i=13. Adding these equations
together, we get a+b+2c+d+2e+f+2g+h+i=52. But we know that the letters are
just the numbers 1, 2, ..., 9 in some order, so a+b+c+d+e+f+g+h+i=45, so
c+e+g=7. Now c, e and g are all different, so the only possibility is
that they are 1, 2 and 4 in some order. If c=1 and e=2, then we'd have
d=10, and that's not possible. So of the three dots c, e and g, the 1
and the 2 must be in ones that aren't next to each other. So we could have
c=1, e=4 and g=2. Now we know that d=8 and f=7, and a+b=12 and
h+i=11, and a, b, h and i are 3, 5, 6 and 9 in some order. So a and
b are 3 and 9, and h and i are 5 and 6, but it could be either way round.
So there are four different solutions, not counting reflections. One is shown
below, and you get the others by switching the two numbers on one end or the
other (or both!).
3 4 5
9 8 7 6
1 2
We can do something very similar if we want the sums to be 14. This time, we
get c+e+g+45=4×14=56, so c+e+g=11. There are several possibilities,
which we'll consider separately.
Case 1: (1,2,8). As above, we can't have 1 and 2 next to each other, so the
only possibility (apart from reflection) is c=1, e=8, g=2. So d=5
and f=4, and a+b=13 and h+i=12, with {a,b,h,i}={3,6,7,9}. So we
get {a,b}={6,7} and {h,i}={3,9}.
Case 2: (1,3,7). This time, we can't have 1 and 3 next to each other either
(as 14-1-3=10), so the only possibility (again not counting reflection) is
c=1, d=6, e=7, f=4, g=3, and we have a+b=13, h+i=11, with
{a,b,h,i}={2,5,8,9}. So {a,b}={5,8} and {h,i}={2,9}, and
there are four possibilities (by swapping ends), of which one is
5 7 2
8 6 4 9
1 3
Case 3: (1,4,6). Now we can't have 4 and 6 next to each other, or we'd need
another 4 in the gap between them (to make 14), so the only possibility is
c=4, d=9, e=1, f=7, g=6, a+b=10, h+i=8, and so we must have
{a,b}={2,8} and {h,i}={3,5}.
Case 4: (2,3,6). This time we can't have 2 and 6 next to each other, so the
only possibilitiy is c=2, d=9, e=3, f=5, g=6, a+b=12, h+i=8, and
so we get {a,b}={4,8} and {h,i}={1,7}.
Case 5: (2,4,5). Now we can't have 4 and 5 next to each other, so the only
possibility is c=5, d=7, e=2, f=8, g=4, a+b=9, h+i=10, and we
get the only solution as {a,b}={3,6}, {h,i}={1,9}.