blog.mathsloth.com/2017/08/worldtop10elementarymathsqns.html
My DD ( primary 1 ) tried the list of questions .. and was 3 for 10. She managed the U.S. question, but the Hong Kong and China's primary 1 questions were slightly too difficult for her. The UK ones - she already knew when her teacher covered briefly with the class.
I have a feeling the standard of maths is unnecessarily high for primary school kids. The world's schools seem to think otherwise.. wonder how kids in other countries cope ..