On a test average (arithmetic mean) test score for 4 students is 85. What must be 5th student's score that average score for 5 students to be 86?
Options.
A) 70
B) 80
C) 90
D) 100
E) 110

Rationale: ( 4 * 85 + x ) / 5 = 86 x = ( 5 * 86 ) - ( 4 * 85 ) x = 430 - 340 total score required 430 - 340 = 90 correct answer is c
Answer: C