Mixed practice: which model? Problem set A Answers

1. (a) Arithmetic (\(d = -2.5\))
2. (b) Geometric (\(r = 1.5\))
3. (c) Neither
4. (d) Geometric (\(r = -\frac{1}{3}\))

\(n = 13\) (\(u_{13} = 41,\ v_{13} \approx 44.6\))

\(3500 + 5 \times 147 = 4235\), so £4235.

Month 20 (A: £1260, B: £1263.48)

\(d = \dfrac{20.0 - 12.0}{4} = 2\); \(u_{10} = 12 + 9(2) = 30\) cm.

(a) A term: \(20 + 14(4) = 76\). (b) A sum: \(\frac{15}{2}(20 + 76) = 720\).

(a) Geometric, r = 3 (b) 1458 (c) 2186