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The total number of leaves on the complete Deca Tree is 10 to the power of 4 which equals 10,000 leaves.

The woodcutter removes

1 trunk = 1000 leaves
1 branch = 100 leaves
1 twig = 10 leaves
1 leaf = 1 leaf

This means the woodcutter removes 1,111 leaves in total.

10,000 minus 1,111 equals 8,889

There are 8,889 leaves remaining on the Deca Tree.

I worked this problem out by reading through it and working out the numbers in my head. It is important to read the question and work through each step.