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|Counting Quadruplets II (Posted on 2010-09-21)
Each of A, B, C and D is a positive integer with the proviso that A ≤ B ≤ C ≤ D ≤ 20
Determine the total number of quadruplets (A, B, C, D) such that: A*B + C*D > 300.
What is the total number of quadruplets (A, B, C, D) such that: A*B - C*D > 100?
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