Of the schools with a mailing state address in California, what is the ratio of the schools located in the county of Colusa against the school located in the county of Humboldt?
Ratio = count(schools in Colusa) / count(schools in Humboldt)
SELECT CAST(SUM(CASE WHEN County = 'Colusa' THEN 1 ELSE 0 END) AS REAL) / SUM(CASE WHEN County = 'Humboldt' THEN 1 ELSE 0 END) FROM schools WHERE MailState = 'CA'