Worksheet Grade 6 Math

Aldermont's Treatment Plant: Turbidity Removal in Percents

A grade 6 worksheet where students track cloudiness through the fictional Aldermont plant and find the percent removed, using decimals and the 0.3 NTU limit.

Grade: Grade 6
Subject: Math
Material: Worksheet
Time: 35 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 2, 5, and 7 have students find what percent of the raw cloudiness is removed, and item 8 splits a blend in a 3 to 1 ratio, the percent-of-a-quantity and ratio work this standard names.

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 1 and 4 require subtracting multi-digit decimal NTU readings using the standard algorithm, exactly the decimal fluency this standard expects.

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 the percent of cloudiness a treatment step removes from water.
Students will subtract and order decimal turbidity readings measured in NTU.

Vocabulary

Turbidity: Turbidity is a measure of how cloudy or murky water looks because of tiny particles floating in it. Clear water has low turbidity, and muddy water has high turbidity.

Also: NTU, percent, ratio

Teacher overview

A treatment plant measures how cloudy water is with a number called turbidity, reported in NTU. Clean finished water must be at or below 0.3 NTU in at least 95 percent of monthly samples and must never rise above 1 NTU. This worksheet follows one batch of water through the fictional Aldermont plant and asks students to find the percent of cloudiness removed at each step. Teaching note: students often divide the change by the wrong number; make sure they compare each drop to the starting, raw cloudiness, not to the smaller finished value.

Aldermont's Treatment Plant: Turbidity Removal in Percents — Grade 6 Math

Name: ____________________________ Date: ______________

Student Worksheet

Water moves through the fictional Aldermont plant in three steps. The raw river water is cloudy. A settling tank removes some cloudiness, and a filter removes most of the rest. The finished water must stay at or below the 0.3 NTU limit.

Raw river water: 12.0 NTU
After the settling tank: 4.5 NTU
Finished water (after the filter): 0.2 NTU

The raw water is 12.0 NTU. After the settling tank it is 4.5 NTU. How much did the cloudiness drop?
What percent of the raw cloudiness did the settling tank remove?
The finished water is 0.2 NTU and the limit is 0.3 NTU. Is the finished water at or below the limit?
From raw (12.0 NTU) to finished (0.2 NTU), how much cloudiness was removed in all?
What percent of the raw cloudiness was removed from start to finish? Round to the nearest tenth of a percent.
The rule says finished water must never rise above 1 NTU. The finished water is 0.2 NTU. How far below 1 NTU is that?
A second batch of raw water reads 15.0 NTU. The plant removes 98 percent of its cloudiness. What is the finished reading?
The plant blends raw river water and clearer spring water in a 3 to 1 ratio. If it uses 300 gallons of river water, how much spring water does it use?
The settling tank alone leaves the water at 4.5 NTU. Explain why that step by itself would not meet the 0.3 NTU limit.
Put these four finished readings in order from lowest to highest: 0.20, 0.25, 0.18, 0.21 NTU.

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: 7.5 NTU.
12.0 - 4.5 = 7.5 NTU of cloudiness removed by the settling tank.
Answer: 62.5 percent.
7.5 ÷ 12.0 = 0.625, and 0.625 × 100 = 62.5 percent of the raw cloudiness.
Answer: Yes.
0.2 NTU is less than the 0.3 NTU limit, so the finished water is at or below the limit.
Answer: 11.8 NTU.
12.0 - 0.2 = 11.8 NTU removed from start to finish.
Answer: 98.3 percent.
11.8 ÷ 12.0 = 0.98333..., and that rounds to 98.3 percent.
Answer: 0.8 NTU.
1 - 0.2 = 0.8 NTU below the 1 NTU ceiling.
Answer: 0.3 NTU.
Removing 98 percent leaves 2 percent behind. 15.0 × 0.02 = 0.3 NTU.
Answer: 100 gallons.
A 3 to 1 ratio means 1 part spring water for every 3 parts river water. 300 ÷ 3 = 100 gallons of spring water.
Answer: It is far above 0.3 NTU.
At 4.5 NTU the water is much cloudier than the 0.3 NTU limit allows, so the filter step is still needed to bring it down.
Answer: 0.18, 0.20, 0.21, 0.25.
Comparing the decimals place by place gives the order 0.18, then 0.20, then 0.21, then 0.25 NTU.

Differentiation

Support

Give students the subtraction already done for item 1 and the division set up for item 2 (7.5 ÷ 12.0). Provide a reminder card that percent removed equals the change divided by the raw value, then multiplied by 100.

Extension

Ask students to imagine a raw batch of 20.0 NTU that must reach the 0.3 NTU limit, then find the smallest percent of cloudiness the plant would need to remove and show their work.

ELL supports

Pair the words "raw," "settling," and "finished" with three clear glasses of water, from muddy to clear, so the vocabulary is visible. Provide the sentence frame: "The plant removed ___ percent because ___."

Extensions

Have students sketch a simple bar for each step (raw, after settling, finished) so the drop in cloudiness is easy to see, then label each bar with its NTU value.