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4MA1/2F Jan 2021, Question 5: Functions as a Mapping

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2F (Foundation) · Calculator · 5 marks

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The question, in short

A number machine applies ×3, then +5, then ÷2 to its input. Find an output, reverse the machine for a given output, and express the output P in terms of input n.

Summarised in our own words. Use the official paper for the exact wording and the diagram.

Part (a) · 1 mark

Starting with input 7, apply the three operations in order and state the resulting output.

  1. 17 × 3 = 21
  2. 221 + 5 = 26
  3. 326 ÷ 2 = 13

Answer13

Part (b) · 2 marks

Given that the final output is 160, work backwards through the operations to determine the original input.

  1. 1160 × 2 = 320
  2. 2320 − 5 = 315
  3. 3315 ÷ 3 = 105

Answer105

Part (c) · 2 marks

With input n, write P as a formula obtained by applying the three operations to n.

  1. 1input n → n × 3 = 3n
  2. 23n + 5
  3. 3(3n + 5) ÷ 2
  4. 4P = (3n + 5)/2

AnswerP = (3n + 5)/2

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