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Date None Specimen Marks available 3 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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