Answer:
Dave drove 168 miles during the 2nd part of the trip
Explanation:
1. Let's review the information given to us to answer the question correctly:
Speed of Dave for part of the trip = 55 mph
Speed of Dave the rest of the trip = 60 mph
Total time of the round trip = 4 hours 12 minutes
Total distance of the trip = 245 miles
2. How far did Dave drive during the 2nd part of his trip?
Let's recall that the formula of speed is:
Speed = Distance/Time, therefore Distance = Speed * Time
x = Time of part of the trip
4 hours 12 minutes - x = Time of the rest of the trip
4.2 hours - x = Time of the rest of the trip
Now, we can write solve for x, this way:
55 * x + 60 (4.2 - x) = 245
55x + 252 - 60x = 245
-5x = 245 - 252
-5x = -7
x = -7/-5 = 7/5 = 1.4 ⇒ 4.2 - x = 2.8
1st part of the trip = 55 * 1.4 = 77 miles
2nd part of the trip = 2.8 * 60 = 168 miles
Dave drove 168 miles during the 2nd part of the trip and 77 miles during the 1st part