| Date | May 2011 | Marks available | 2 | Reference code | 11M.1.sl.TZ2.1 |
| Level | SL only | Paper | 1 | Time zone | TZ2 |
| Command term | Find | Question number | 1 | Adapted from | N/A |
Question
In an arithmetic sequence, \({u_1} = 2\) and \({u_3} = 8\) .
Find d .
Find \({u_{20}}\) .
Find \({S_{20}}\) .
Markscheme
attempt to find d (M1)
e.g. \(\frac{{{u_3} - {u_1}}}{2}\) , \(8 = 2 + 2d\)
\(d = 3\) A1 N2
[2 marks]
correct substitution (A1)
e.g. \({u_{20}} = 2 + (20 - 1)3\) , \({u_{20}} = 3 \times 20 - 1\)
\({u_{20}} = 59\) A1 N2
[2 marks]
correct substitution (A1)
e.g. \({S_{20}} = \frac{{20}}{2}(2 + 59)\) , \({S_{20}} = \frac{{20}}{2}(2 \times 2 + 19 \times 3)\)
\({S_{20}} = 610\) A1 N2
[2 marks]
Examiners report
This question was answered correctly by the large majority of candidates. The few mistakes seen were due to either incorrect substitution into the formula or simple arithmetic errors. Even where candidates made mistakes, they were usually able to earn full follow-through marks in the subsequent parts of the question.
This question was answered correctly by the large majority of candidates. The few mistakes seen were due to either incorrect substitution into the formula or simple arithmetic errors. Even where candidates made mistakes, they were usually able to earn full follow-through marks in the subsequent parts of the question.
This question was answered correctly by the large majority of candidates. The few mistakes seen were due to either incorrect substitution into the formula or simple arithmetic errors. Even where candidates made mistakes, they were usually able to earn full follow-through marks in the subsequent parts of the question.
