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jmc

counting and probability senior

Problem

Let be the number of ordered quadruples of positive odd integers that satisfy Find
Solution
Define . Then , so . So we want to find four natural numbers that sum up to 51; we can imagine this as trying to split up 51 on the number line into 4 ranges. This is equivalent to trying to place 3 markers on the numbers 1 through 50; thus the answer is , and .
Final answer
196