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Number Theory

How many ordered pairs of integers $(a,b)$ are there, such that $100 \leq a \leq 1000, 100 \leq b \leq 1000$ and

$\frac{a}{b} = \frac{12}{21}?$

Details and Assumptions:

For an ordered pair of integers $(a,b)$ , the order of the integers matter. The ordered pair $(1, 2)$ is different from the ordered pair $(2,1)$ .