Cristina drove at an average speed of 35 mi/h from her home in San Diego to visit her sister in Dallas.

Question

Cristina drove at an average speed of 35 mi/h from her home in San Diego to visit her sister in Dallas. She stayed in Dallas 20 hours, and on the tripback averaged 40 mi/h. She returned home 44 hours after leaving.How many miles is San Diego from Dallas?

Answer 1

Let d be the distance. She took d/35 hours to travel to SD and d/40 hours to return.

d/35 + d/40 + 20 = 44 -> 8d/280 + 7d/280 = 24 -> 8d +7d = 6720 -> 15d = 6720 -> d = 448