Foundation November 2018 Paper 3 Q22
22
\[k = n^2 + 9n + 1\]Mo says,
“\(k\) will be a prime number for all integer values of \(n\) from 1 to 9”
Show that Mo is wrong.
You must show that your value of \(k\) is not prime. [3 marks]
| Answer | Mark | Comments |
|---|---|---|
| Any correct value | M1 | 11, 23, 37, 53, 71, 91, 113, 137, 163 |
| Selects 91 as the only incorrect value with no errors in values given | A1 | oe eg stops at 91 |
| 91 and 13 (is a factor) or 91 and 7 (is a factor) or 91 and \(13 \times 7\) | A1 | oe eg \(91 \div 7 = 13\) |
Additional guidance
| Ignore incorrect evaluations for first mark | |
| Ignore all values for \(n\) greater than 9 | |
| Do not allow 11 within a list of prime numbers eg 2, 3, 5, 7, 11… | |
| Error in list eg 12, 23, 37, 53, 71, 91, 113, 137, 163 with 12 and 91 selected as not prime (not valid as incorrect) | M1A0A0 |
| Error in list eg 12, 23, 37, 53, 71, 91, 113, 137, 163 with only 91 selected as not prime (not valid as incorrect conclusion from their list) | M1A0A0 |
| \(9^2 + 9 + 1 = 91\) is incorrect working | M0A0A0 |