A person travels by car from one city to another. She drives for 23.5 min at 74.5 km/h, 15.9 min at 111 km/h, 49.2 min at 38.7 km/h, and spends 17.3 min along the way eating lunch and buying gas. Determine the distance between the cities along this route. Answer in units of km.

The product of speed and time is distance. To calculate the total distance you multiple the speed in kilometers per second by the time at that speed in seconds, do this for all 3 different speeds then add them up, the 17.4 minutes eating does not affect the answer at all. to convert from minutes to seconds multiply time in minutes by 60, to convert from km/h to km/s divide km/h by 3600.

(23.5x60) x (74.5/3600) = 29.2km (rounded to 1 decimal place)

+

(15.9x60) x (111/3600) = 29.4km (rounded to 1 decimal place)

+

(49.2x60) x (38.7/3600) = 31.7km

=90.3km

The brackets are not necessary but i think it makes it more clear what is happening in your working.