Answer:
1 (first circle), 4 (second circle)
Explanation:
In the first circle if you multiply the central number, 5, with any number in the top-half of the circle, you get the number opposite it in the bottom half of the circle. For example, if you multiply 5 with 3, you get 15, which is directly opposite to 3 in the circle.
In the second circle, if you multiply the central number, 3, with any number in the bottom-half of the circle, you get the number opposite it in the top-half of the circle. For example, if you multiply 3 with 5, you get 15, which is directly opposite 5 in the circle.
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