On a test average (arithmetic mean) test score for 9 students is 80. What must be 10th student's score that average score for 10 students to be 82?  Choose the correct choice from the following answers
A) 100 B) 90 C) 80 D) 70 E) 60

Rationale: "( 9 * 80 + x ) / 10 = 82 x = ( 10 * 82 ) - ( 9 * 80 ) x = 820 - 720 total score required 820 - 720 = 100 correct answer is a"
Answer: A