Speed, Distance, Time
Part of the Decimals, Percents & Ratios section of Coddy's Pre-Algebra journey. Lesson 44 of 56.
Speed is a unit rate: distance per hour. A bus at 40 km/h covers 40 km in every hour it drives. In 4 hours that is 40 + 40 + 40 + 40, which is 40 × 4, or 160 km.
So distance = speed · time. The same fact turns around two ways: speed = distance / time, which is the unit rate from the last lessons, and time = distance / speed. Write down which two you know, and the third follows.
The units must match. A speed in km per hour needs a time in hours: 30 minutes at 40 km/h is half an hour, so the bus covers 20 km, not 40 × 30. Multiplying km per hour by hours leaves km, which is why the answer comes out as a distance.
Challenge
A car drives at a steady 65 km/h for 3 hours. Find the distance d it covers, in km. Write d equal to the calculation, then work it out on the next line.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Decimals, Percents & Ratios
4Dividing Decimals
Dividing by a DecimalDividing by 10 and 100Dividing by a Whole NumberUnit PriceRecap: Dividing2Adding Decimals
Adding DecimalsSubtracting DecimalsNegative DecimalsMaking ChangeRecap: Add and Subtract