Find n (A) for A={0,1,2,3, ...,2000}

There are 2001 items in that set.

So n (A) = 2001

We can individually count them all out, which is very slow and tedious, or we can use the formula

n-m+1

where,

m = starting value

n = ending value

In this case,

m = 0

n = 2000

So,

n-m+1 = 2000-0+1 = 2001

This formula only works if we increase the number by 1 each time (eg: 6, 7, 8, etc)