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VTMO 2022 — Grade 6 — vtmo Question 6

VTMO · VTMO 2022 — Grade 6 — vtmo

Question 6

How many two-digit numbers $ab$ have both $a + b$ and $a - b$ prime?
  1. $9$
  2. $10$
  3. $12$
  4. $18$
  5. $24$