17 Alan has to attend a meeting on Monday and on Tuesday. The probability that he is late for a meeting is \(\dfrac{1}{8}\)
(a) Complete the probability tree diagram.(3)
(b) Calculate the probability that Alan is late for at least one of these meetings. (3)
Mark scheme (a)
Scheme
Marks
\(\frac{7}{8}\) for not late
B1
Correct binary structure
B1
ALL labels and values correct
B1
(3)
Notes
B1: on lower first branch
B1: 4 branches needed on RHS
Apart from questions 5b, 8, 15d, 20b, 21b, 23, 24b (where the mark scheme states otherwise) the correct answer, unless clearly obtained by an incorrect method, should be taken to imply correct working.
Mark scheme (b)
Scheme
Marks
(1/8) × “(7/8)” or “(7/8)” × (1/8) or (1/8) × (1/8)
M1 ft
(1/8) × “(7/8)” + “(7/8)” × (1/8) +(1/8) × (1/8)
M1 ft
\(\dfrac{15}{64}\)
A1
(3)
(Total 6 marks)
Notes
M1 ft: Any 1 “correct” product
M1 ft: 3 “correct” products with intention to add. Only ft probabilities < 1 or M2 for 1 −“\((\frac{7}{8})^2\)”
