Worksheet Grade 11 Engineering & Design

Selby Reach Monitoring Data: Turbidity and Chlorine Statistics

A grade 11 worksheet where students compute the mean, median, and range of a week of turbidity and chlorine readings and compare them to treatment standards.

Grade: Grade 11
Subject: Engineering & Design
Material: Worksheet
Time: 35 min
Prep: No prep
Materials: Calculator

Standards

HSS-ID.A.2 Common Core Math

Use statistics appropriate to the shape of the data distribution to compare center (median, mean) and spread (interquartile range, standard deviation) of two or more different data sets.

How this material aligns: Items 2 through 4 have students find the mean, median, and range of a week of turbidity readings to describe the data's center and spread, exactly what this standard requires.

All materials for HSS-ID.A.2 →

HSN-Q.A.3 Common Core Math

Choose a level of accuracy appropriate to limitations on measurement when reporting quantities.

How this material aligns: Item 8 asks students to report a chlorine residual only to the accuracy the test kit supports, matching reported precision to the instrument as this standard directs.

All materials for HSN-Q.A.3 →

Download Word file

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 mean, median, and range of a set of daily water-quality readings.
Students will compare monitoring results to a treatment standard and report values to an appropriate accuracy.

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.
Chlorine residual: Chlorine residual is the small amount of chlorine still left in the water after it leaves the treatment plant. It keeps protecting the water from germs all the way to your faucet.

Also: mean, median, range

Teacher overview

Operators at the fictional Selby Reach treatment plant record finished-water turbidity and chlorine residual every day. This worksheet gives students one week of those readings and asks them to summarize the data with the mean, median, and range, then compare the results to the standards a real plant must meet. Working with a small, realistic dataset is how students see why summary statistics matter to plant operators.

Selby Reach Monitoring Data: Turbidity and Chlorine Statistics — Grade 11 Engineering & Design

Name: ____________________________ Date: ______________

Student Worksheet

Use these readings from one week at the fictional Selby Reach plant for all items.

Daily turbidity (NTU): 0.10, 0.12, 0.14, 0.11, 0.15, 0.13, 0.10
Daily chlorine residual (mg/L): 0.90, 1.10, 0.80, 1.00, 1.20, 0.70, 1.00

List the seven turbidity readings in order from least to greatest.
Find the mean turbidity for the week. Round to the nearest hundredth NTU.
Find the median turbidity for the week.
Find the range of the turbidity readings.
This plant must keep turbidity at or below 0.3 NTU in nearly all of its samples. Did every reading this week meet the 0.3 NTU limit? How do you know?
Find the mean chlorine residual for the week. Round to the nearest hundredth mg/L.
Systems usually keep the distribution residual between 0.2 and 2.0 mg/L. Are all seven residual readings inside that range?
A test kit reads chlorine to the nearest 0.1 mg/L. A student writes a residual as 0.9300 mg/L. Rewrite that value so its accuracy matches the kit.
Using the mean and range you found for turbidity, explain why one unusually high reading in a week would be easy to notice in this dataset.
For a public water-quality report, is the mean or the range a better single description of the week's turbidity? Explain your choice.

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: 0.10, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15 NTU. The two readings of 0.10 come first, then the values rise to the highest reading of 0.15.
Answer: 0.12 NTU. The seven readings sum to 0.85, and 0.85 divided by 7 is 0.1214, which rounds to 0.12 NTU.
Answer: 0.12 NTU. In the ordered list the fourth of seven values is the middle one, which is 0.12 NTU.
Answer: 0.05 NTU. The range is the highest reading minus the lowest, 0.15 minus 0.10, which is 0.05 NTU.
Answer: yes. The highest reading all week was 0.15 NTU, which is below the 0.3 NTU limit, so every day met the standard.
Answer: 0.96 mg/L. The seven residual readings sum to 6.70, and 6.70 divided by 7 is 0.957, which rounds to 0.96 mg/L.
Answer: yes. The lowest residual was 0.70 mg/L and the highest was 1.20 mg/L, so all seven fall inside the 0.2 to 2.0 mg/L range.
Answer: 0.9 mg/L. The kit is accurate only to the nearest 0.1 mg/L, so 0.9300 mg/L should be reported as 0.9 mg/L.
Answer: Accept any answer noting that the readings cluster near 0.12 NTU with a small range of 0.05 NTU, so a reading much higher than about 0.15 NTU would stand out clearly against that tight cluster.
Answer: Accept either choice with sound reasoning; the strongest answers note that the mean gives a typical value for the week while the range only shows the spread, so the mean better summarizes overall performance.

Differentiation

Support

Provide the ordered turbidity list already written for item 1 so students can focus on the mean, median, and range. Give a printed reminder of how to find each statistic, with a small non-water example worked through.

Extension

Ask students to compute the mean turbidity a second week would need for the two-week average to land at exactly 0.13 NTU, then explain what a rising average might tell an operator at the fictional plant.

ELL supports

Provide a labeled example showing the words "mean," "median," and "range" with a tiny three-number dataset. Allow students to answer items 9 and 10 with a sentence frame: "The ___ is a better summary because it shows ___."