Easy -1.2 This is a straightforward arithmetic sequence question requiring only recognition of the pattern (4, 7, 10, 13, ...) and direct application of the standard sum formula S_n = n/2(2a + (n-1)d). It involves minimal problem-solving—just substitution into a memorized formula with n=100, a=4, d=3.
6 A sequence is given by
$$\begin{gathered}
a _ { 1 } = 4 \\
a _ { r + 1 } = a _ { r } + 3
\end{gathered}$$
Write down the first 4 terms of this sequence.
Find the sum of the first 100 terms of the sequence.
B1 for \(d = 3\) soi. B1 for \(a = 4\) soi. M1 for use of \(100/2[2a + 99d]\) o.e.
5 marks
$4, 7, 10, 13, 16$ ignore extras | B1 | For showing 1st four or 2nd four terms
$15250$ | B4 | B1 for $d = 3$ soi. B1 for $a = 4$ soi. M1 for use of $100/2[2a + 99d]$ o.e.
| | 5 marks |
6 A sequence is given by
$$\begin{gathered}
a _ { 1 } = 4 \\
a _ { r + 1 } = a _ { r } + 3
\end{gathered}$$
Write down the first 4 terms of this sequence.\\
Find the sum of the first 100 terms of the sequence.
\hfill \mbox{\textit{OCR MEI C2 2005 Q6 [5]}}