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(Source: Asian Maths Olympiad 2015, Year 3)

Given the first two circles, what's the answer in the blank space?

I've tried using all basic operations but no pattern seems to work for all three.

Any help would be greatly appreciated.

P.S. Is there a formal name for this type of puzzle?

  • $\begingroup$ What is the source of this puzzle? Puzzles without proper attribution may be deleted. $\endgroup$
    – hexomino
    Aug 20 '20 at 16:04
  • $\begingroup$ A friend sent this, so I had to look it up. But source has been added. $\endgroup$ Aug 20 '20 at 17:41

After staring at it for a few more minutes, I figured it out.

The product of the numbers in the top "row" should be equal to the sum of the bottow "row"
Ex. For the first circle, 6 x 4 = 15 + 9
Thus, the blank space is equal to 11.


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