مسئله ابغى كيف حلها

[الحمد الله على كل حال]

student takes a 7 questions multiple choice quiz with 4 choices for each question. answer the following two questions.
1) what is the standard deviation of the number of correct answers??????
2) what is the mean number of incorrect answers????????????????

كيف طريقة
وكمان ليه عرفتوا انها بانونومبل هوا اخر درس بشبتر خمسه