Question

how many four digit number are there in all​

Answer 1

9999 is the right answer

Answer 2

Answer:

9000

Explanation:

It is A.P. related problem. {A.P.=1000,1001,1002,-----9999}

a=1000

d=1

an=9999

n=?

using formula:an=a+(n-1)d

9999=1000+(n-1)1

or

n=9000