Elapsed Time and Base-Sixty Regrouping
Time arithmetic regroups at sixty (seconds, minutes) and at twelve/twenty-four (hours, AM/PM), with days and weekdays cycling on top. Problems find elapsed time between clock readings, future dates, and the error of a fast or slow clock. It is place-value regrouping in a mixed-base system.
grade 2–3 Measurement & dataOperations Draw a DiagramWork Backwards
Progression (10)
g2 1. Compare hours first, then minutes Measurement & data
g1 2. Find a future date using days per month Measurement & data
g3 3. Elapsed time between two clock times Measurement & data
g3 4. Reason about a fast or slow clock Measurement & data
g3 5. Reach the next hour, then add the rest Measurement & data
g3 6. Read a mirrored clock, then find elapsed time Measurement & data
g2 7. Read the hour when the hand is between Measurement & data
g3 8. AM and PM make a 24-hour day Measurement & data
g3 9. A drifting clock accumulates daily error Measurement & dataOperations
g3 10. Time regroups in base sixty Measurement & data
Bridges to competition (5)
Reasoning problems that extend this idea toward competition:
Round-Trip Elapsed Time Other
Daylight length from sunrise and sunset Other
Train timetables and elapsed time Pattern & rule
Convert between clock time systems Other
Find a city's time from the offset Other