You've solved the first one . . .
A sum of 100 cannot be produced by one throw.1. A dartboard is divided into 6 sections.
These 6 sections is given numbers: 49, 5, 54, 28, 37, 23.
What is the least number of throws needed in order to get a score of exactly 100?
I have noticed that a sum of 100 can be the sum of 3 numbers: 23 + 23 + 54.
. . So you found a three-number sum . . . Good!
And it can be shown that a sum of 100 cannot be produced by two throws.
. . [Just check out the 15 two-number sums.]
Therefore, at least three throws are needed . . . That's it!