To factor the expression \( 100x + 1000 \) completely, we can start by finding the greatest common factor (GCF) of the terms.
The GCF of \( 100x \) and \( 1000 \) is \( 100 \). We can factor out \( 100 \) from the expression:
\[ 100x + 1000 = 100(x + 10) \]
Thus, the expression \( 100x + 1000 \) factored completely is:
\[ 100(x + 10) \]