Number Patterns and Arithmetic Sequences
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Number Patterns and Arithmetic Sequences — Free MYP5 Mathematics (Extended) Practice Questions

1QuestionDeriving the nth Term of an Arithmetic SequenceConcept Practice
3 marks~5 minCriterion A
A city's public bike-share programme tracks registered users over four consecutive months. The data form an arithmetic sequence:

Month (nn)1234
Users (unu_n, hundreds)471013


These points are plotted on a graph with nn on the horizontal axis and unu_n on the vertical axis.
a
Explain how the graph shows that the common difference is d=3d = 3. [1]
b
Deduce the formula for unu_n, the number of users (in hundreds) in month nn. [1]
c
The programme's funding is renewed only if registered users exceed 5 000 before the end of month 18. Justify whether this funding condition is met. [1]
Question diagram

Solutions

2QuestionFinding the Common DifferenceAssessment Practice
6 marks~9 minCriterion D
A bank offers a loan of 10 000 dollars to be repaid over 10 months. The monthly repayments follow an arithmetic sequence. The first payment is 1 200 dollars and each subsequent payment decreases by a fixed amount, so that the tenth payment is 300 dollars.
a
Show that the common difference of the repayment sequence is −100-100 dollars. [2]
b
Calculate the total amount repaid over the 10 months. [1]
c
Advise the bank whether this repayment plan should be offered to borrowers, discussing what the total repayment implies about interest or fees and how real-world factors such as variable interest rates or late-payment penalties affect the reliability of this model. [3]
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Solutions

3QuestionSolving Problems Using Arithmetic SequencesAssessment Practice
16 marks~24 minCriterion B
Communication: Arithmetic Series and Staircase Patterns

A staircase is being built using identical blocks. The number of blocks required for each step forms an arithmetic sequence.

The pattern begins as follows:

Step number: 1, 2, 3, 4, …
Blocks in step: 3, 5, 7, 9, …

Let SnS_n represent the total number of blocks needed to build a staircase with nn steps.

Question
a
Calculate S1S_1, S2S_2, S3S_3, and S4S_4. Show clearly how each total is formed from the blocks in each step. [4 marks]
b
Predict a general formula for SnS_n in terms of nn. Your answer should:

- Identify the pattern in the totals,
- Express the relationship using algebra,
- Clearly define what nn and SnS_n represent. [4 marks]
c
Justify your formula by showing that SnS_n can be written as the sum of the first nn terms of an arithmetic series. In your response:

- Identify the first term aa,
- Identify the common difference dd,
- Write the nnth term of the sequence,
- Use the arithmetic series sum formula,
- Simplify your expression to match your formula from part (b). [6 marks]
d
Derive the standard formula for the sum of an arithmetic series: Sn=n2[2a+(n−1)d]S_n = \frac{n}{2} [2a + (n-1)d]. Use clear mathematical communication and explain each step of your derivation. [4 marks]

(e) Explain why clear notation is important when solving this problem, especially the difference between:

- Blocks in the nnth step,
- Total blocks in nn steps. [2 marks]

Solutions

4QuestionDeriving the nth Term of an Arithmetic SequenceAssessment Practice
6 marks~9 minCriterion C
A student records weekly savings (in dollars) over four weeks:

Week 1: 15 — Week 2: 22 — Week 3: 29 — Week 4: 36

A friend claims the nnth term of this arithmetic sequence is un=8n+7u_n = 8n + 7.
a
Calculate the values predicted by un=8n+7u_n = 8n + 7 for Weeks 1 to 4. [2]
b
Deduce, with supporting calculations, whether the formula un=8n+7u_n = 8n + 7 correctly models the student's savings. [2]
c
The student has a savings goal of 100 dollars in a single week. Using the correct nnth term formula, justify whether this goal will ever be reached exactly under the same saving pattern. [2]

Solutions

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