Question: a student finds the sum 1 + 2 + 3 + . . . as his patience runs out . he found the sum as 575 . when the teacher declared the result wrong , the student realized that he missed a number . what was the number the student missed ?
A) 16
B) 18
C) 14
D) 20
E) 22
Correct answer: d
Grade: 7 | Topic: Number System | Difficulty: Hard | Standard: 7.NS.A.3