Moderate -0.3 This is a straightforward arithmetic progression question requiring standard formulas (nth term and sum). The first part involves solving two simultaneous equations, which is routine. The second part requires calculating S_50 - S_20, which is slightly less standard but still a direct application of the sum formula. Overall, slightly easier than average due to being purely procedural with no conceptual challenges.
The third term of an arithmetic progression is 24. The tenth term is 3.
Find the first term and the common difference.
Find also the sum of the 21st to 50th terms inclusive. [5]
Simplify
Question 5:
5 | a+2d = 24 and a + 9d = 3
d = −3; a = 30
S − S
50 20
−2205 cao | M1
A1
A1
M1
A1 | if M0 , B2 for either, B3 for both
ft their a and d;
M1 for S = (u + u ) o.e.
30 21 50
B2 for -2205 www | do not award B2 or B3 if values clearly obtained
fortuitously
S = −2175; S = 30
50 20
u = 30 20 × 3 = 30
21
u = 30 49 × 3 = 117
50
The third term of an arithmetic progression is 24. The tenth term is 3.
Find the first term and the common difference.
Find also the sum of the 21st to 50th terms inclusive. [5]
Simplify
\hfill \mbox{\textit{OCR MEI C2 Q5 [5]}}