Rationale
Sam could have seen 14 movies last year.
Given the range of movies watched by Sam, Lucy, and his friends is 10, Sam's number of movies must fit within the limits established by the highest and lowest counts among the friends plus Lucy's total. The highest number of movies seen by Sam's friends is 17 and the lowest is 9; thus, Sam’s possible movie count must be between 9 and 19, allowing for Lucy’s count to remain valid.
A) If Sam saw 14 movies, Lucy would have seen 7 fewer, totaling 7 movies. The range in this case would be from 7 (Lucy's count) to 17 (the highest count among friends), which gives a range of 10 (17 - 7 = 10), fitting the condition perfectly.
B) If Sam saw 15 movies, Lucy would have seen 8 movies. The range would then be from 8 to 17, which results in a range of 9 (17 - 8 = 9), failing to meet the required range of 10.
C) If Sam saw 16 movies, Lucy would have seen 9 movies. The range would be from 9 to 17, giving a range of 8 (17 - 9 = 8), which again does not satisfy the range condition of 10.
D) If Sam saw 17 movies, Lucy would have seen 10 movies. The range would stretch from 10 to 17, leading to a range of only 7 (17 - 10 = 7), failing to fulfill the requirement of a 10 range.
E) If Sam saw 18 movies, Lucy would have seen 11 movies. The range would be from 11 to 17, resulting in a range of 6 (17 - 11 = 6), which does not align with the necessary range of 10.
Conclusion
To meet the established range of 10 movies among Sam, Lucy, and his friends, Sam must have seen 14 movies. This choice allows for Lucy's count of 7 movies, ensuring the range between the highest and lowest counts remains at 10. All other options fail to meet this essential criterion.