Great Granddad is very proud of his telegram from the Queen
congratulating him on his hundredth birthday and he has friends who
are even older than he is... When was he born?
Place the numbers 1, 2, 3,..., 9 one on each square of a 3 by 3
grid so that all the rows and columns add up to a prime number. How
many different solutions can you find?
In this 7-sandwich: 7 1 3 1 6 4 3 5 7 2 4 6 2 5 there are 7 numbers between the 7s, 6 between the 6s etc. The article shows which values of n can make n-sandwiches and which cannot.
There are exactly 3 ways to add 4 odd numbers to get 10.
Re-arranging the order of the numbers does not give a new solution.
Find all the ways of adding 8 odd numbers to get 20. To be sure of
getting all the solutions you will need to be systematic. What
about a total of 15 with 6 odd numbers?