Californians have long complained that the state doesn’t adequately fund education. But last week, they still opted not to amend a 40-year-old property tax formula that could have added roughly $4 billion a year to the state’s education budget. Proposition 15 divided the state in half, with official results released Wednesday showing it fell 51.8 percent against to 48.2 percent in favor. The measure would have altered 1978’s Proposition 13 — known for inspiring a tax revolt across the country — and based commercial and industrial property taxes on market rates instead of purchase price.