∴ Its normal curve is symmetrical about the straight line x= 1000,

Also, the number of people with grades between 80- 100 accounts for about 13 of the total number.

According to symmetry, the number of students with a score of not less than 120 is about 12- 13= 16 of the total number of students.

Students with a score of not less than 16× 1200=200 probably have 120.

So the answer is: 200.