To simplify the expression \( t^{400} \cdot t^{100} \) using the Quotient Rule of Integer Exponents, we apply the product of powers property, which states that when multiplying like bases, we add the exponents:
\[ t^{400} \cdot t^{100} = t^{400 + 100} = t^{500}. \]
So, the simplified expression is:
t500 (or \( t^{500} \)).