Why 78%?

Yin Wood is 乙, a climbing vine; Yang Wood is 甲, a tall tree. Both are Wood, so the pair starts at 76. One is yang and one is yin, which adds +2: 76 + 2 = 78.

Out of the 10 stems, 5 would score higher with Yin Wood.

Only the year's stem is used — this is a quick game, not a saju (Four Pillars) reading. The points are our own design; the five-element cycles are a tradition, not a science.