There are 20 questions in a multiple choice exam, each with 4 answers and only one is correct. The students are guessing the answers in an independent way. Correct answer = +5, incorrect answer = -1, unaswered = 0. What is the expected value of the grades, what is the variance of the grades and what is the probabilty to get the same grade as the expected value?

The answers are: 10, 135, 0.2.
I tried binomic distrubiton: p = 0.125 (0.5 if the students choose to answer the question and 0.25 if they're right) but I don't get the correct answers.

Thank you.

it should be a and d. lmk if i'm wrong xd

answer: what are the following choices

step-by-step explanation:

the triangles are similar. therefore the corresponding sides are in proportion:

              cross multiply

            divide both sides by 32

1,407.5 hours

step-by-step explanation:

we first convert all the time to hours and then sum them up.

there are 24 hours in 1 day, in 58 days, there are 24 x 58 = 1,392 hours.

there are 60 minutes in 1 hour, thus, 30 minutes will be equivalent to 30 / 60 = 0.5 hours.

therefore, the number of hours it will take mercury to complete a full rotation is 1,392 + 15 + 0.5 = 1,407.5 hours