2014 · Q29
p, q and r are prime numbers such that p < q < r < 13. In how many cases would (p + q + r) also be a prime number?
Elementary MathematicsNumber System
- A1
- B2
- C3
- DNone of the above
Explanation
p + q + r must be odd, so all three are odd primes from {3, 5, 7, 11}: 3+5+11 = 19 and 5+7+11 = 23 are prime — 2 cases.