They value the entire chunk, then base the 10% on it. Your question makes it sound as if they said 10% is worth 800M, then 90% is worth 9 times as much. The log

They value the entire chunk, then base the 10% on it. Your question makes it sound as if they said 10% is worth 800M, then 90% is worth 9 times as much. The logic would be 100% cost 8B, so 10% cost $800M.