To simplify the expression \( t^{400} \div t^{100} \) using the Quotient Rule of Integer Exponents, you subtract the exponent in the denominator from the exponent in the numerator:
\[ t^{400} \div t^{100} = t^{400 - 100} = t^{300} \]
So, the simplified expression is \( t^{300} \).