Determine Start or End Time Using a Number Line
Determine Start or End Time Using a Number Line is a Grade 3 math skill from Eureka Math using the relationship Start Time + Duration = End Time in both directions. To find an unknown end time, add the duration to the start time. To find an unknown start time, subtract the duration from the end time. A number line models each jump forward or backward in time. Third graders use this strategy to solve elapsed time problems with unknown start or end times, making abstract time arithmetic visual and systematic.
Key Concepts
To find an unknown end time, add the duration to the start time: $$Start\ Time + Duration = End\ Time$$ To find an unknown start time, subtract the duration from the end time: $$End\ Time Duration = Start\ Time$$.
Common Questions
How do you find the end time when you know the start time and duration?
Add the duration to the start time: End Time = Start Time + Duration. On a number line, jump forward from the start by the duration amount.
How do you find the start time when you know the end time and duration?
Subtract the duration from the end time: Start Time = End Time - Duration. On a number line, jump backward from the end by the duration amount.
Give an example of finding an end time.
An activity starts at 1:15 PM and lasts 45 minutes. End time = 1:15 + 0:45 = 2:00 PM. On the number line, jump 45 minutes forward from 1:15.
Give an example of finding a start time.
A movie ends at 4:30 PM and lasted 90 minutes. Start time = 4:30 - 1:30 = 3:00 PM. On the number line, jump 90 minutes backward from 4:30.
In which textbook is Determine Start or End Time Using a Number Line taught?
This skill is taught in Eureka Math, Grade 3.