SOLUTION: In a high school year book, there is a picture of each pair of students in the graduating class, and a picture of each student in the graduating class. There are a total of 1275 pi
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Question 397320: In a high school year book, there is a picture of each pair of students in the graduating class, and a picture of each student in the graduating class. There are a total of 1275 pictures. What is the sum of the digits of the number of students in the graduating class?
Choose the answer and explain the reason to choose your response:
7
6
8
5
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
Let 
represent the number of students. Then the number of pairs of students is the number of combinations of things taken 2 at a time, or !}\ =\ \frac{n(n-1)}{2})
. And there are 1275 pictures so:
}{2}\ +\ n\ =\ 1275)
Multiply by 2, distribute, collect terms, and move the constant into the LHS:
Solve for the positive root and then add the digits of the number of students.
John
My calculator said it, I believe it, that settles it
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