A true-false test consists of 20 questions, each of which has one correct answer: true, or false. One point is awarded for every correct answer, but one point is taken off for each wrong answer. Suppose a student answers every question by guessing at random, independently of other questions. Let S be the student’s score on the test.
1-Find E(S)
2-Find SE(S)
3-Find (no approximations, please) P(S=0)

Question

A true-false test consists of 20 questions, each of which has one  correct answer: true, or false. One point is awarded for every correct answer, but one point is taken off for each wrong answer. Suppose a student answers every question by guessing at random, independently of other questions. Let S be the student’s score on the test.
1-Find E(S)
2-Find SE(S)
3-Find (no approximations, please) P(S=0)

anonymous · Answer

E(S)=0

anonymous · Answer

$$P(S=0)=\frac{1}{2^{10}}$$

anonymous · Answer

thank you! i needed it for homework!

anonymous · Answer

THANK YOU SOOO MUCH! The lecturer was rambling on with a prewritten script, and I couldn't understand most of what she was saying!

anonymous · Answer

the standard error score cannot be calculated like this

kropot72 · Answer

@lucky12345 I agree. Therefore my attempt has been deleted.

anonymous · Answer

@kropot72 ans is wrong plzzzz help

anonymous · Answer

Find SE(S) ? help please

anonymous · Answer

SE(S)= 4.472


E(S-E(S))= 20-0 =20

E(S-E(S)) POWER 2 = 20 POWER 2 = 400

=400*0.05 =20 =SQRT OF 20 =4.472

anonymous · Answer

P(S=0) ans is 0.1761

anonymous · Answer

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anonymous · Answer

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anonymous · Answer

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