Time Detectives Slides TEKS 3.7C Math Sleuths
Grade 3 Mathematics
Solving Elapsed-Time Mysteries
Time Detectives
Crack the case of start times, elapsed minutes, and comparing when different friends finish!
Mission: Find finish times using open number lines
Case File: Elapsed Time
STEP 1
The Jump Strategy Toolkit
Open Number Lines
1. Pin Start Time
Locate where the clock begins on the left side of your number line.
Example: 10:00 a.m.
2. Jump Person 1
Make curved jumps for the first person's elapsed minutes to find their finish time.
Jump +30 min → 10:30
3. Jump Person 2
Start from Person 1's finish time and jump the extra minutes to reach the end!
Jump +15 min → 10:45
Key Clue: "15 minutes after Veronica" means add 15 minutes to Veronica's finish time, not the test start time!
CASE 01
The Math Test Mystery
Guided Practice
"A test started at 10:00 a.m. Veronica finished in 30 minutes . Kiana finished 15 minutes after Veronica . What time did Kiana finish?"
Visual Number Line Model
+30 min (Veronica)
+15 min (Kiana)
10:00 a.m.
Test Begins
10:30 a.m.
Veronica Finishes
10:45 a.m.
Kiana Finishes!
Solution: 10:00 + 30 min = 10:30 a.m. → 10:30 + 15 min = 10:45 a.m. Solved!
CASE 02
The Great Recess Relay
Five-Minute Increments
"The recess relay race started at 1:15 p.m. Marcus completed the course in 25 minutes . Tasha crossed the finish line 20 minutes after Marcus . What time did Tasha finish?"
Step 1: Marcus's Time
Start Time: 1:15 p.m.
Jump: + 25 minutes
1:15 + 25 min = 1:40 p.m.
Step 2: Tasha's Time
Marcus Finish: 1:40 p.m.
Jump: + 20 minutes
1:40 + 20 min = 2:00 p.m.
Notice: 40 minutes + 20 minutes = 60 minutes, which bumps us to the next hour (2:00 p.m. )!
CASE 03
The Science Fair Experiment
Comparing Elapsed Times
"The science lab opened at 9:40 a.m. Andre finished his project in 35 minutes . Maya finished 25 minutes after Andre . What time did Maya finish her project?"
Detective Clue: Break Jumps into Friendly Numbers!
Andre's Finish:
9:40 + 20 min = 10:00 a.m.
10:00 + 15 min = 10:15 a.m.
Maya's Finish:
10:15 + 25 min = 10:40 a.m.
(Total elapsed: 60 minutes!)
Pro Tip: Jumping to the nearest whole hour (like 10:00) makes mental math fast and error-free!
Detective Protocol Summary
Ready for Independent Practice
1
Find & Circle the Start Time
Always record the exact start time at the far left tick mark of your timeline.
2
Calculate the First Person's Finish Time
Jump their duration forward. Label their finish time clearly in the middle.
3
Add the Comparative Minutes
Jump forward from Person 1 to find Person 2's final finish time.
Now open your Time Detectives Practice Worksheet and solve each mystery! Good luck, Sleuths! →
Time Detectives Worksheet Time Detectives Worksheet
TEKS 3.7C • Elapsed Time & Comparative Finish Times
Name:
Date:
Detective Strategy: 1. Plot Start Time → 2. Jump 1st Person's Minutes → 3. Jump 2nd Person's Extra Minutes
Part 1: Cases 1–3
Case 1
A math test started at 10:00 a.m. Veronica finished in 30 minutes. Kiana finished 15 minutes after Veronica. What time did Kiana finish?
Show your timeline jumps: Start: 10:00 a.m.
10:00 a.m. Veronica's Finish: _______ Kiana's Finish: _______
Veronica finished at: ____________
Kiana's Finish Time:
Case 2
Art class began painting at 1:15 p.m. Leo completed his portrait in 25 minutes. Sam finished his portrait 20 minutes after Leo. What time did Sam finish?
Show your timeline jumps: Start: 1:15 p.m.
1:15 p.m. Leo's Finish: _______ Sam's Finish: _______
Leo finished at: ____________
Sam's Finish Time:
Case 3
Students started reading in the library at 11:10 a.m. Caleb read for 35 minutes. Priya finished reading 15 minutes after Caleb. What time did Priya finish?
Show your timeline jumps: Start: 11:10 a.m.
11:10 a.m. Caleb's Finish: _______ Priya's Finish: _______
Caleb finished at: ____________
Priya's Finish Time:
Time Detectives • Grade 3 Mathematics TEKS 3.7C Page 1 of 2 → Turn over for Cases 4–6
Time Detectives: Advanced Cases
Multi-Step Clues • Crossing the Hour • Challenge Case
Page 2
Case 4
A computer lab challenge began at 2:15 p.m. Noah solved his puzzle in 30 minutes. Layla solved her puzzle 25 minutes after Noah. What time did Layla finish?
Show your timeline jumps (watch the hour mark!): Start: 2:15 p.m.
2:15 p.m. Noah's Finish: _______ Layla's Finish: _______
Noah finished at: ____________
Layla's Finish Time:
Case 5 • Challenge
The school relay race started at 10:05 a.m. Runner A finished in 15 minutes. Runner B finished 20 minutes after Runner A. Runner C finished 10 minutes after Runner B. What time did Runner C finish?
Show all 3 jumps on your timeline: Start: 10:05 a.m.
10:05 a.m. Runner A: _____ Runner B: _____ Runner C: _____
A: ________ • B: ________
Runner C's Finish Time:
Case 6 • Sleuth Creator
Write your own elapsed-time mystery! Fill in the blanks with your own times and names, then solve it below.
A ______________________ started at _______:_______ a.m./p.m.
Time Detectives Answer Key Time Detectives Answer Key
Teacher Guide • TEKS 3.7C Worked Solutions
TEACHER ANSWER KEY • Page 1
Key Misconception Alert: Students often mistakenly add the second person's minutes to the original start time instead of the first person's finish time.
Case 1 Solution
Start: 10:00 a.m. • Veronica: 30 minutes • Kiana: 15 minutes after Veronica
10:45 a.m.
Step 1 (Veronica): 10:00 a.m. + 30 min = 10:30 a.m.
Step 2 (Kiana): 10:30 a.m. + 15 min = 10:45 a.m.
Timeline model: Two jumps (+30 min, then +15 min). Total elapsed time from start is 45 minutes.
Veronica: 10:30 a.m.
Correct Answer: 10:45 a.m.
Case 2 Solution
Start: 1:15 p.m. • Leo: 25 minutes • Sam: 20 minutes after Leo
2:00 p.m.
Step 1 (Leo): 1:15 p.m. + 25 min = 1:40 p.m.
Step 2 (Sam): 1:40 p.m. + 20 min = 2:00 p.m.
Teacher Note: Highlight that 40 min + 20 min = 60 min, meaning the clock rolls forward to exactly the next hour (2:00 p.m.).
Leo: 1:40 p.m.
Correct Answer: 2:00 p.m.
Case 3 Solution
Start: 11:10 a.m. • Caleb: 35 minutes • Priya: 15 minutes after Caleb
12:00 p.m.
Step 1 (Caleb): 11:10 a.m. + 35 min = 11:45 a.m.
Step 2 (Priya): 11:45 a.m. + 15 min = 12:00 p.m. (noon)
Teacher Note: Accept either "12:00 p.m." or "12:00 noon". Point out the change from a.m. to p.m.
Caleb: 11:45 a.m.
Correct Answer: 12:00 p.m. (noon)
Time Detectives Teacher Key • TEKS 3.7C Page 1 of 2 → See Page 2 for Cases 4–6
Time Detectives Answer Key (Pt. 2)
Advanced Cases 4–6 • Scoring Rubric
TEACHER ANSWER KEY • Page 2
Case 4 Solution
Start: 2:15 p.m. • Noah: 30 minutes • Layla: 25 minutes after Noah
3:10 p.m.
Step 1 (Noah): 2:15 p.m. + 30 min = 2:45 p.m.
Step 2 (Layla): 2:45 p.m. + 25 min = 2:45 + 15 min (3:00) + 10 min = 3:10 p.m.
Crossing the hour: Breaking 25 min into (+15 to reach 3:00) and (+10 past 3:00) is the recommended TEKS strategy.
Noah: 2:45 p.m.
Correct Answer: 3:10 p.m.
