Final answer:
Marco's family will likely arrive first because his average speed is higher than Valerie's.
Step-by-step explanation:
To determine who will likely arrive first, we need to compare the time it will take each person to reach their destination. Since speed is given in miles per hour, we can use the formula:
Time = Distance / Speed
Let's assume the distance to their grandparents' house is the same for both Valerie and Marco. Since Valerie's average speed is 47.5 miles per hour and Marco's average speed is 55 miles per hour, Valerie's speed is lower and it will take her more time to cover the same distance. Therefore, Marco's family will likely arrive first.