Converting Units
Part of the Decimals, Percents & Ratios section of Coddy's Pre-Algebra journey. Lesson 45 of 56.
An hour is 60 minutes. A film runs 90 minutes: how many hours is that? Every 60 minutes make one hour, so divide by 60: 90 / 60 is 3/2, an hour and a half.
The rule: changing to a bigger unit, divide by the conversion number; changing to a smaller unit, multiply. 3 hours is 3 × 60, which is 180 minutes. Why? A bigger unit holds more, so fewer of them fit in the same time. Hours are big, so there are fewer hours than minutes.
A conversion is itself a rate: 60 minutes per hour, 100 centimetres per metre, 1000 metres per kilometre. Ask which unit is bigger, and the direction follows. A quick check helps: your answer in the bigger unit must be the smaller number.
Challenge
A cooking class lasts 150 minutes. Find the time h in hours. Write h equal to the calculation, then work it out on the next line. A fraction and a decimal are both fine answers.
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: Dividing