I'm in the UK, and I don't think it's fair to be singling out teachers on this.
I work with retailers - we make eCommerce systems - and I never cease to be staggered at how many CFOs/finance people/buyers/business owners don't:
- Know the difference between "gross" and "net" when talking about prices, tax, or margin.
- Know how to calculate a percentage. What's 10% off £90? No idea.
- Virtually all fall for the "mark it down by 10%, then mark it up by 10%... same price!" fallacy.
- Completely fail to grasp statistics. "Me" is not a statistically significant sample size.
So long as Western society treats mathematical literacy with contempt, this will only get worse - and treat it with contempt we do, for if you are able to figure out the average of two single digit numbers in your head, you are a "braniac" or a "geek", which is fucking incomprehensible.