| Date | None Specimen | Marks available | 2 | Reference code | SPNone.2.sl.TZ0.1 |
| Level | SL only | Paper | 2 | Time zone | TZ0 |
| Command term | Find | Question number | 1 | Adapted from | N/A |
Question
In an arithmetic series, the first term is −7 and the sum of the first 20 terms is 620.
Find the common difference.
[3]
a.
Find the value of the 78th term.
[2]
b.
Markscheme
attempt to substitute into sum formula for AP M1
e.g. \({S_{20}} = \frac{{20}}{2}(2( - 7) + 19d)\) , \(\frac{{20}}{2}( - 7 + {u_{20}})\)
setting up correct equation using sum formula A1
e.g. \(\frac{{20}}{2}(2( - 7) + 19d = 620\)
\(d = 4\) A1 N2
[3 marks]
a.
correct substitution \( - 7 + 77(4)\) A1
\({u_{78}} = 301\) A1 N2
[2 marks]
b.
Examiners report
[N/A]
a.
[N/A]
b.
Syllabus sections
Topic 1 - Algebra » 1.1 » Arithmetic sequences and series; sum of finite arithmetic series; geometric sequences and series; sum of finite and infinite geometric series.
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