Problem
Change the unit using a decimal
A car covers a known distance in a time given in hours and minutes. We need the distance it covers in one hour.
Number systemRatios
Your answer
How to solve
Strategy Analyze the Units — The distance is per hour, so the time has to be measured in hours before anything can be divided. Minutes are sixtieths of an hour, and turning them into a decimal is the whole first half of the problem.
1STEP 1
Turn the minutes into part of an hour
There are 60 minutes in an hour, so divide the minutes by 60.
48 ÷ 60 = 0.8
The trip took 1.8 hours.
6.NS.B.3Analyze The Unitsminutes is of an hour.
Why?
An hour is always the same minutes, so a stretch of minutes can be renamed as a part of an hour without changing what it measures.
🧱A bigger unit is a fixed count of smaller unitsA bigger unit always equals the same fixed number of smaller units (1 hour = 60 minutes, 1 km = 1000 m), so a measure can be renamed between them.
2STEP 2
Divide the distance by the time
The distance in one hour is the whole distance shared over the hours taken.
160 ÷ 1.8 = 88.888…
The quotient does not end.
6.RP.A.2Work Backwards3STEP 3
Round to one decimal place
Look at the second decimal place to decide: it is 8, so the first decimal place rounds up.
88.88… ≈ 88.9
The car covers about 88.9 km in an hour.
5.NBT.A.4Organize Information In More WaysAnswer
88.9 km
Multiply back: 88.9 × 1.8 ≈ 160.0 km, matching the distance given.
Takeaway
Minutes are sixtieths of an hour -- turn them into a decimal before dividing.
- Turn the minutes into part of an hour
- Divide the distance by the time
- Round to one decimal place