To rewrite the sum \(25 + 75\) using their greatest common factor (GCF) and multiplication, we first need to find the GCF of 25 and 75.
The GCF of 25 and 75 is 25. Now we can factor out the GCF from the sum:
\[ 25 + 75 = 25 \times 1 + 25 \times 3 \]
This simplifies to:
\[ 25 + 75 = 25(1 + 3) \]
So, the expression can be rewritten as:
\[ 25 + 75 = 25 \times 4 \]
Since \(25 \times 4 = 100\), this matches the original equation \(100 = 25 + 75\).