39961

My solution is 8,7,13,10,6,12,9

First I made all the the number bonds to 15 . Then I tried 1 and 15 which did not work, I then realised that the first number must be above 5 because when you need to add up to 20 you only have the numbers up to 15. So then I tried 5 and 10 which also didn't work because you needed another 10 to make 20. Next I tried 6 and 9 which did not work once again because I needed one of the numbers I had already used. After that I tried 7 and 9 which also didn't work because then again I needed one of the numbers I'd already used. Finally I tried 8 and 7 which worked !!!! (FINALLY)