When Yunji added all the integers from 1 to 9, she mistakenly left out a number. Her incorrect sum turned out to be a square number. Which number did Yunji leave out?
Answer Choices
A. 5
B. 6
C. 7
D. 8
E. 9
When Yunji added all the integers from 1 to 9, she mistakenly left out a number. Her incorrect sum turned out to be a square number. Which number did Yunji leave out?
Answer Choices
A. 5
B. 6
C. 7
D. 8
E. 9