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PrintSouth African Mathematics Olympiad
South Africa number theory
Problem
One of the factors of is chosen at random. What is the probability that the chosen factor is NOT a multiple of ?
(A) (B) (C) (D) (E)
(A) (B) (C) (D) (E)
Solution
There are ten factors: , , , , , , , , , . Four of them are not multiples of , viz. , , , . The probability is therefore or .
Final answer
A
Techniques
Factorization techniques