যোগে যোগে জোড় বিজোড় | Math Problem

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Why isn't the answer...

Why isn’t the answer 5? For instance,

16 + 4 = 20
20 + (50 + 31) = 101
101 + (60 + 40) = 201

16, 4, 50, 60, 40 – five of them are even