| Exam Board | OCR MEI |
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| Module | Paper 3 (Paper 3) |
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| Year | 2019 |
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| Session | June |
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| Topic | Proof |
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5 A student's attempt to prove by contradiction that there is no largest prime number is shown below.
If there is a largest prime, list all the primes.
Multiply all the primes and add 1.
The new number is not divisible by any of the primes in the list and so it must be a new prime.
The proof is incorrect and incomplete.
Write a correct version of the proof.