Problem: The positive integers $d_1, d_2, .. d_n $divide 1995. Prove that there exist $d_i $and $d_j $among them, suach that the numerator of the reduced fraction $d_i$/$d_j $is at least n.
Solution. Note that 3 · 5 · 7 · 19 = 1995. If the chosen divisors include
one divisible by 19 and another not divisible by 19, the quotient of the two
has numerator divisible by 19, solving the problem since n ≤ 16. If this is
not the case, either all divisors are or divisible by 19 or none of them has
this property, and in particular n ≤ 8. Without loss of generality, assume
the divisors are all not divisible by 19.
Under this assumption, we are done if the divisors include one divisible
by 7 and another not divisible by 7, unless n = 8. In the latter case all of
the divisors not divisible by 19 occur, including 1 and 3 · 5 · 7, so this case
also follows. We now assume that none of the chosen divisors is divisible
by 4, so that in particular n ≤ 4.
Again, we are done if the divisors include one divisible by 5 and another
not divisible by 5. But this can only fail to occur if n = 1 or n = 2. The
former case is trivial, while in the latter case we simply divide the larger
divisor by the smaller one, and the resulting numerator has at least one
prime divisor and so is at least 3. Hence the problem is solved in all cases

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