ANSWER:
30 trips
STEP-BY-STEP EXPLANATION:
To calculate the remainder we can propose the following equation
[tex]\begin{gathered} 20+1\cdot x=50 \\ \text{where x is the number of trips} \end{gathered}[/tex]Solving for x:
[tex]\begin{gathered} 20+x=50 \\ x=50-20 \\ x=30 \end{gathered}[/tex]