IB Maths AA HL AA 1.1 Sequences and series questions

Exam-style questions in the shape of Paper 1 and Paper 2, with full markschemes. Read the markscheme, or type, photograph or draw your answer and get it marked.

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Paper 1, no calculator Paper 2, calculator

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Question 1

Paper 2, calculatorMedium12 marks

A small hydroelectric station records its annual electricity generation to the nearest GWh. Figure 1 shows the recorded generation in years 1 to 6.

Let $v_n$ be the generation, in GWh, predicted for year $n$ by an arithmetic sequence model. The model is chosen so that its first and sixth terms match the recorded generation in years 1 and 6.

(a)

Calculate the increase in recorded generation from year 2 to year 3, and from year 5 to year 6.

[2]

(b)

Determine the first term $a$ and common difference $d$ of the model.

[3]

(c)

Hence, estimate the generation predicted by the model for year 9.

[2]

(d)

Write the total generation predicted by the model over the first nine years in sigma notation, and determine its value.

[3]

(e)

Comment on the suitability of this model for estimating generation in year 9, referring to the plotted data.

[2]

Question 2

Paper 2, calculatorMedium6 marks

A convergent geometric series has first term 8 and common ratio $r$ The sum of its first three terms is 14.

(a)

Determine $r$

[4]

(b)

Hence determine the sum to infinity of the series.

[2]

An employer models an employee’s salary at the start of each year using a geometric sequence. The salary at the start of year 1 was $40,000, and the salary at the start of year 5 was $48,620.25. Let $u_n$ denote the modelled salary, in dollars, at the start of year $n$

(a)

State the first term and determine the positive common ratio.

[2]

(b)

Determine the modelled salary at the start of year 9, to the nearest cent.

[2]

(c)

Hence write the total of the modelled salaries for the first nine years as a sum in sigma notation, and determine this total to the nearest cent.

[2]

(d)

State one reason why this model may become unreliable when used to predict salaries many years into the future.

[1]

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