Worksheet Grade 6 Math

Marrowbrook's Wells and the PFOA Limit: A Percent Worksheet

A grade 6 worksheet comparing four fictional Marrowbrook wells' PFOA readings with the 4.0 ppt federal limit using percent, ratio, and decimal reasoning.

Grade: Grade 6
Subject: Math
Material: Worksheet
Time: 30 min
Prep: No prep
Materials: Calculator (optional)

Standards

6.RP.A.3 Common Core Math

Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations, including finding a percent of a quantity and converting measurement units.

How this material aligns: Items 1, 2, 6, and 10 have students find a percent of the 4.0 ppt limit and read percents above 100, the ratio and percent reasoning this standard targets.

All materials for 6.RP.A.3 →

6.NS.B.3 Common Core Math

Fluently add, subtract, multiply, and divide multi-digit decimals using the standard algorithm for each operation.

How this material aligns: Items 4 and 5 require subtracting and averaging multi-digit decimal ppt readings, the standard-algorithm decimal fluency this standard expects at grade 6.

All materials for 6.NS.B.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 calculate what percent of a legal limit a measured value represents.
Students will rank and compare decimal contaminant readings from cleanest to highest.

Vocabulary

PFAS: A large family of human-made chemicals used in things like nonstick pans, waterproof fabric, and firefighting foam. They are called forever chemicals because they take a very long time to break down.
Parts per trillion: A unit for measuring extremely small amounts of a chemical in water. PFAS limits are set in parts per trillion because these chemicals matter even in tiny doses.

Also: percent, ratio

Teacher overview

The federal limit for PFOA, one of the PFAS chemicals, is 4.0 ppt (parts per trillion). This worksheet uses the fictional town of Marrowbrook, which tested four wells, to practice percent, ratio, and decimal work. PFAS rules are still changing, so present the rule as one in motion: the 4.0 ppt limit set in 2024 is not proposed to change, while EPA has proposed letting eligible water systems apply for a two-year exemption, from April 2029 to April 2031, a proposal that was not yet final as of September 2026. Teaching note: before students begin, remind them that a reading can be more than 100 percent of a limit, which simply means the value sits above the limit.

Marrowbrook's Wells and the PFOA Limit: A Percent Worksheet — Grade 6 Math

Name: ____________________________ Date: ______________

Student Worksheet

In the fictional town of Marrowbrook, the water team tested four wells for PFOA. The federal limit is 4.0 ppt. Here are the four readings:

Well A: 3.0 ppt
Well B: 6.0 ppt
Well C: 5.2 ppt
Well D: 2.0 ppt

Well A reads 3.0 ppt. What percent of the 4.0 ppt limit is that?
Well B reads 6.0 ppt. What percent of the limit is that?
Which wells are above the limit? Explain how you know.
Well C reads 5.2 ppt. How many ppt is Well C above the limit?
The town mixes equal amounts of Well A water and Well D water. What is the PFOA level of the mix?
What percent of the limit is the mixed water from item 5?
Write the ratio of Well D's reading to the limit in simplest form.
Rank the four wells in order from the cleanest reading to the highest reading.
A well reads 150 percent of the limit. Explain in one sentence what that tells the town.
The town sets a safety goal of 50 percent of the limit. What reading in ppt equals that goal?

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: 75 percent.
3.0 ÷ 4.0 = 0.75, and 0.75 × 100 = 75 percent.
Answer: 150 percent.
6.0 ÷ 4.0 = 1.5, and 1.5 × 100 = 150 percent. A value above 100 percent means the reading is above the limit.
Answer: Wells B and C.
Well B (6.0 ppt) and Well C (5.2 ppt) are both higher than the 4.0 ppt limit. Wells A and D are below it.
Answer: 1.2 ppt.
5.2 - 4.0 = 1.2 ppt above the limit.
Answer: 2.5 ppt.
The mix is the average of the two wells: (3.0 + 2.0) ÷ 2 = 5.0 ÷ 2 = 2.5 ppt.
Answer: 62.5 percent.
2.5 ÷ 4.0 = 0.625, and 0.625 × 100 = 62.5 percent.
Answer: 1 to 2.
Well D reads 2.0 ppt and the limit is 4.0 ppt. The ratio 2 to 4 reduces to 1 to 2.
Answer: D, A, C, B.
In order of reading: Well D 2.0, Well A 3.0, Well C 5.2, Well B 6.0. The cleanest is Well D and the highest is Well B.
Answer: It sits above the limit.
150 percent of the limit is more than 100 percent, so the reading is above the 4.0 ppt limit, and the town would need to treat or blend that water, or stop using the well, to meet the rule.
Answer: 2.0 ppt.
50 percent of 4.0 is 0.50 × 4.0 = 2.0 ppt.

Differentiation

Support

Give students the division already set up for items 1, 2, and 6 (each reading divided by 4.0) and a reminder that "percent" means "out of 100." Allow a calculator for the decimal steps so the focus stays on the meaning of each answer.

Extension

Ask students to imagine a fifth well that sits at exactly 90 percent of the limit, then show the calculation that proves the reading is 3.6 ppt. Have them explain whether that well would pass or fail the limit and by how much.

ELL supports

Pre-teach "limit," "reading," and "percent" with a simple number line running from 0 up to the 4.0 ppt limit and beyond it. Let students point to where each well falls on the line before they write full sentences.

Extensions

Have the class compare Marrowbrook's simple four-well table to the way a real state posts its drinking-water test results, and discuss why a clear table helps residents understand their own water.