Math problem set Grade 4 Math

Tealwood Filter Washes: Hours, Minutes, and Seconds

A grade 4 problem set following a fictional filter plant's wash schedule, converting hours to minutes and minutes to seconds and solving two-step crew problems.

Grade: Grade 4
Subject: Math
Material: Math problem set
Time: 35 min
Prep: No prep
Materials: None

Standards

4.MD.A.1 Common Core Math

Know relative sizes of measurement units within one system of units including km, m, cm; kg, g; lb, oz; l, ml; hr, min, sec. Within a single system of measurement, express measurements in a larger unit in terms of a smaller unit. Record measurement equivalents in a two-column table.

How this material aligns: Problems 1, 3, 4, 5, and 6 express a larger unit in a smaller one, changing minutes to seconds, hours to minutes, and meters to centimeters.

All materials for 4.MD.A.1 →

4.OA.A.3 Common Core Math

Solve multistep word problems posed with whole numbers and having whole-number answers using the four operations, including problems in which remainders must be interpreted. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding.

How this material aligns: Problems 7 and 8 are multistep, and problem 8 requires interpreting a remainder as one additional worker needed for the shift.

All materials for 4.OA.A.3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will express hours in minutes and minutes in seconds for a plant's wash schedule.
Students will solve two-step problems combining a wash time and a check time.
Students will explain why a measurement in a smaller unit uses a larger number.

Vocabulary

Backwash: Backwash is when a treatment plant reverses the flow of water through a filter to flush out the dirt and particles it has trapped. It is like rinsing out a dirty sponge so the filter can keep working well.

Also: filter, convert, unit, shift

Teacher overview

The fictional Tealwood Filter Plant sends river water through six sand filters before the water is piped to homes. Sand traps dirt, so every filter has to be washed clean on a schedule, and the crew logs each wash in a different unit depending on which form they are filling out. This problem set follows one Saturday of washing and asks students to move between hours, minutes, and seconds for the same events. The misconception to watch for is the belief that a measurement written in a smaller unit should be a smaller number, which leads students to divide by 60 when changing 12 minutes into seconds instead of multiplying.

Tealwood Filter Washes: Hours, Minutes, and Seconds — Grade 4 Math

Name: ____________________________ Date: ______________

Problems

One filter wash at Tealwood takes 12 minutes. How many seconds is that?
The crew washes 6 filters, one after another. Each wash takes 12 minutes. How many minutes does the whole set of washes take?
Use your answer to problem 2. How many seconds is that many minutes?
On Saturday the crew runs 3 hours of washing in all. How many minutes is that?
One filter run between washes lasts 2 hours and 15 minutes. How many minutes is that?
The pipe from the filter to the wash tank is 3 meters long. How many centimeters is that?
Each filter takes 12 minutes to wash and 28 minutes to check afterward. The crew works through 5 filters. How many minutes does that take?
There are 23 filter washes still on the list. One worker can finish 5 washes in a shift. How many workers are needed so that all 23 washes are done in one shift?
A new worker wrote in the log that 180 minutes is the same as 3 minutes. Explain the mistake and write the correct match.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: 720 seconds.
One minute is 60 seconds, so 12 minutes is 12 × 60. Splitting 12 into 10 + 2 gives 10 × 60 = 600 and 2 × 60 = 120, and 600 + 120 = 720 seconds.
Answer: 72 minutes.
Six washes at 12 minutes each is 12 × 6 = 72 minutes.
Answer: 4,320 seconds.
72 × 60. Splitting 72 into 70 + 2 gives 70 × 60 = 4,200 and 2 × 60 = 120, and 4,200 + 120 = 4,320 seconds.
Answer: 180 minutes.
Three hours at 60 minutes each is 3 × 60 = 180 minutes.
Answer: 135 minutes.
Two hours is 2 × 60 = 120 minutes. Adding the extra 15 minutes gives 120 + 15 = 135 minutes.
Answer: 300 centimeters.
One meter is 100 centimeters, so 3 meters is 3 × 100 = 300 centimeters.
Answer: 200 minutes.
Each filter needs 12 + 28 = 40 minutes of crew time. Five filters need 40 × 5 = 200 minutes.
Answer: 5 workers.
23 ÷ 5 gives 4 with a remainder of 3, because 5 × 4 = 20 and 3 washes are still waiting. Four workers would leave 3 washes undone, so a fifth worker is needed even though that worker finishes only 3 washes.
Answer: The worker dropped the unit, since 180 minutes is the same as 3 hours, not 3 minutes.
Minutes are smaller than hours, so the number of minutes must be larger than the number of hours. Accept any answer that states 180 minutes equals 3 hours and explains that the smaller unit needs the larger number.

Differentiation

Support

Provide a two-column table with 1 hour, 2 hours, and 3 hours already matched to 60, 120, and 180 minutes so students can extend the pattern rather than start from zero. Let students skip-count by 60 on a number line for problems 1 and 3.

Extension

Ask students to write the whole Saturday schedule from problem 4 in seconds, then explain in two sentences why the plant's log uses minutes instead of seconds for daily work.

ELL supports

Pre-teach "wash," "shift," "convert," and "unit" alongside a picture of a filter with an arrow showing water moving through sand. Provide the sentence frame: ___ hours is the same as ___ minutes because 1 hour equals 60 minutes.

Extensions

Have students time a classroom routine such as lining up, record it in seconds, and then write the same length of time in minutes and seconds, explaining which form is easier to read.