Explanation:

Now, the numbers which lie between 1000 and 10000 are actually all 4 digits numbers
So, we need to find all 4 digit numbers that can be formed by using the given digits : 1, 3, 5, 6, 7, 8, 9
Therefore, The required numbers which can  be formed without repetition of the digits :
No. of digits = 7
Number of possibilities = 4
So, Total numbers which can be formed = 7 × 6 × 5 × 4=840