self Maths Puzzle

1 day the principal summoned 1000 students in the quad.. there are 1000 aligned lunch box in the quad..
The principal asked Student number 1 to open every single lunch box, from 1-1000. and asked Student number 2 to come in and close every even lunch box (2,4,6 etc until 1000).
and asked Student number 3 to go to every 3rd lunch box and opens it f its close, and closes it if it s open.
and the 4th student will go to every 4th lunch box and opens it if its close, closes it if its open..
and continues until the 1000th student..
Q: after the 1000th student.. what do u think is the exact number of open lunch-boxes? why?

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self Other Question
A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father? Let n be the number of different 5 digit numbers, divisible by 4 with the digits 1, 2, 3, 4, 5 and 6, no digit being repeated in the numbers. What is the value of n?