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jmc

algebra senior

Problem

The equation has positive integer solutions where is a positive single digit. How many such s exist? (Since is representing a digit, if then represents the integer 20.)
Solution
We need to find two numbers with a product of and a sum of , where is a positive single digit. There are only 9 digits to try for . Suppose we have a product of 10 and a sum of 11, then the two numbers could be 1 and 10. Suppose we have a product of 20 and a sum of 12, then the two numbers are 2 and 10. This will work for all values of from 1 to 9, so there are of that work.
Final answer
9\text{ values}