That cannot be correct.

4*5 = 20
2*1 = 2
3*2 = 6

20+2+6 = 28

4+2+3 = 9

28 / 9 = 2,9(around.. 27 / 9 = 3, so 28 / 9 should be slightly less than 3).

Final algorythm:
(4*5) + (2*1) + (3*2) / (4+2+3)

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