Answer:
1.844
Step-by-step explanation:
Given that final exam has 20 multiple choices questions. 10 questions have 5 choices and 10 questions have 4 choices.
So we divide the questions into two groups I and II.
The no of correct answers in I is called U.
U is binomial with n =10 and p = 0.2
Similarly II group, V the no of correct answers would be binomial
with n =10 and p = 0.25
Our random variable X= U+V
Obviously U and V are independent.
We have var (U) = npq = 1.6
Var (V) = npq = 1.875
Var(X) = Var(U+V)
= Var(U)+Var(V) since U and V are independent
= 3.4
STd dev (X) = [tex]\sqrt{3.4} \\=1.844[/tex]
