10 (a) The first 5 terms of a sequence are given below. 4 -2 1 -0.5 0.25

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

1. [1] (a)(i) 4×(-0.5)^19
2. [1] (a)(i) -1/131072 or -7.63×10^-6 or -7.62939...×10^-6 rot to four or more figs
3. [1] (a)(ii) Valid explanation e.g. the common ratio is between -1 and 1
4. [1] (a)(ii) 4/(1-(-0.5)) = 8/3
5. [1] (b)(i) a+9d=15(a+d)
6. [1] (b)(i) 6/2 {2a+5d} = 87
7. [1] (b)(i) Solves their equations for d e.g. 2(-3/7 d) + 5d = 29
8. [1] (b)(i) d=7
9. [1] (b)(ii) a = -3 soi
10. [1] (b)(ii) 6990 = their(-3)+(n-1)(their7)
11. [1] (b)(ii) n = 1000