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Question 1

Given numbers: 3, 5, 7, 10
Result of expression: 12
Number of possible orderings and choices of operators:

Question 2

Given numbers: 1, 1, 3, 9
Result of expression: 5
Number of possible orderings and choices of operators:

Question 3

Given numbers: 1, 2, 5, 9
Result of expression: 20
Number of possible orderings and choices of operators:

Questions and suggestions to Frank.Luebeck@Math.RWTH-Aachen.De.