Is high school level math/science being taught well in North America?

I'm constantly worried whether I should educate my children in school in North America or back home in south-east asia. I'm mostly worried that my kids won't be able to grasp the basic math/science skill as I've seen many students at undergrad level lack proper logic when I was a TA.

I stumbled upon this

http://classroom.synonym.com/solve-percentages-numbers-17430.html?wa_user1=tombstone

The proper solution could be

Question: 30% of 15 = ?

Answer:

30% of 100 = 30

30% of 1 = 30/100

30% of 15 = (30/100)15

           = (3/10)15
 
           = (9/2) = 4.5

The rot logic of creating decimal and not teaching important logic for students who are just learning basics of math bothers me. Wondering if this kind of thing is prevalent ?