Hi plaksha,

For getting admissions in high school in New York you have to appear in the SHSAT which stands for specialized higher school admission test.

This test is basically for getting admissions in classes 8th to 10th in the high schools of New York or students of united nations who wish to get admission there.

The test comprises of 2 sections that is:

1.Comprehensive 

2.Verbal/maths

And this whole exam consists of total 800 marks out of which minimum marks to be scored is 400.

Each year about 30000 to 40000 students appear for this exam but only 3000 to 4000 students gets the admission.

The the exam is conducted between the months of october to april.

And for maths portion just focus on the syllabus of class 7th or 8th maths.

Good luck.