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1.6.13 Standard formulae for arithmetic series (A-level only)

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Question 15

A start-up company tracks its daily net cash flow, CnC_nCn​, in pounds (£\pounds£). The cash flow follows an arithmetic sequence with first term aaa and common difference ddd.

The total net cash flow over the first 12 days is £\pounds£ 432.

a.

Show that 4a+22d=1444a + 22d = 1444a+22d=144.

[3]
b.

Given that the total net cash flow over the first 30 days is £\pounds£ 0, determine the total net cash flow over the first 15 days.

[4]
c.

SnS_nSn​ represents the sum of the daily net cash flow for the first nnn days. Explain why the value you calculated in part (b) is the maximum value of SnS_nSn​.

[2]

1.6.13 Standard formulae for arithmetic series (A-level only) Questions

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