Unit 6
4 marks · Easy(a) The sequence S = {3, 6, 12, 24, ...} shows the number of bacteria in a sample at the end of each hour. The number triples every two hours. (b) Let D be the set of all values in S less than 25.
Write down the 4th term in sequence S.
List all the elements of the set D.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 24
(b) {3, 6, 12, 24}
Common mistakes: incorrect term progression; omitting elements
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Identifies or computes each term in the correct sequence.
A1 (a) · 1 mark · Final answer 24 for the 4th term.
M1 (b) · 1 mark · Lists set of all values in S less than 25.
A1 (b) · 1 mark · All correct values complete for D: {3,6,12,24}.
Worked solution
(a) S = 3, 6, 12, 24,... So the 4th term is 24.
(b) S less than 25 is {3, 6, 12, 24}.