Question 689265: there are 6 MC questions in a short quiz and 5 options are given for each question. 2 marks are awarded for a correct answer and 1 mark is deducted for a wrong answer. If a student answers the questions by guessing, find the probability that
a. his total scoreis is negative;
b. his total scoreis is zero;
c. his total scoreis is postive.
Answer by vleith(2983)   (Show Source):
You can put this solution on YOUR website! If the student simply guesses on each question, he has a 20% chance of guessing correctly (1 chance in 5) and and 80% chance of guessing incorrectly (4 chances in 5).
So what are the points at those odds?
The student has 20% at 2 points. Or 0.2*2 = 0.4 per question
The student has 80 at -1 points. Or 0.8 * (-1) = -0.8 per question
Net, pure guessing is a losing deal here.
If the student could correctly eliminate one potential answer before guessing, he breaks even. If he can eliminate 2 potential answers before guessing, he comes out ahead.
FYI ... SAT is scored with negative points for an incorrect answer. For SAT hints on guessing see
http://www.math.com/students/kaplan/sat_intro/guess2.htm
Answer A
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