A quiz has three questions, with each question worth one mark. If 20% of the students
got 0 questions correct, 5% got 1 question correct, 40% got 2 questions correct, and
35% got all 3 questions correct, then the overall class mean (average) mark was
(A) 1.8
(B) 1.9
(C) 2
(D) 2.1
(E) 2.35

Question

A quiz has three questions, with each question worth one mark. If 20% of the students
got 0 questions correct, 5% got 1 question correct, 40% got 2 questions correct, and
35% got all 3 questions correct, then the overall class mean (average) mark was
(A) 1.8
(B) 1.9
(C) 2
(D) 2.1
(E) 2.35

hartnn · Answer

you can use the formula : 
$\large Mean=\dfrac{m_1x_1+m_2x_2+m_3x_3+m_4x_4}{m_1+m_2+m_3+m_4}$

where m's are the % of people getting 'x' question correct.

anonymous · Answer

hartnn is right, very good manipulation of logic and combination of other formula. He treated the percentages as the number of students