Worksheet Grade 7 Science

Brackham's Lead Samples: Reading a 10-Home Tap Test

A grade 7 science worksheet: students read lead results from 10 homes, find the percent above the action level, and judge if the sample fits the town.

Grade: Grade 7
Subject: Science
Material: Worksheet
Time: 35 min
Prep: No prep
Materials: Calculator

Standards

MS-ESS3-3 NGSS

Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.

How this material aligns: Items 1 through 5 have students read a tap-sampling program that monitors lead pollution in drinking water and decide whether the town must act.

All materials for MS-ESS3-3 →

7.RP.A.3 Common Core Math

Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.

How this material aligns: Items 2 and 4 use percent reasoning to find the share of sampled homes above each action level, the multistep percent work this standard names.

All materials for 7.RP.A.3 →

7.SP.A.1 Common Core Math

Understand that statistics can be used to gain information about a population by examining a sample of the population; generalizations about a population from a sample are valid only if the sample is representative of that population.

How this material aligns: Item 9 asks whether 10 homes fairly represent a town of 4,000, the reasoning about representative samples this statistics standard requires.

All materials for 7.SP.A.1 →

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 find the percent of sampled homes above a regulatory action level.
Students will compute the median and range of a small data set.
Students will judge whether a sample is large enough to represent a population.

Vocabulary

Lead (Pb): A soft gray metal that is poisonous, especially for children. It can get into drinking water from old pipes and plumbing, so utilities work hard to control it.
Action level: A trigger number in lead and copper testing. If too many homes test above this level, the utility must take steps like improving treatment and telling the public.
Service line: A service line is the small pipe that connects the water main under the street to the plumbing inside one home or building. It is the last leg of the trip water makes to your tap.

Also: parts per billion, median

Teacher overview

Lead can dissolve into tap water from old service lines, the small pipes that connect a house to the water main. EPA estimates that about 4 million lead service lines remain in US water systems. Utilities test a set of homes and compare the results to an action level, which is 15 parts per billion now and drops to 10 parts per billion in 2027. This worksheet uses results from the fictional town of Brackham, where an operator sampled 10 homes. Students find how many homes are above each action level, compute the center of the data, and judge whether 10 homes can speak for the whole town.

Brackham's Lead Samples: Reading a 10-Home Tap Test — Grade 7 Science

Name: ____________________________ Date: ______________

Student Worksheet

Suppose the town of Brackham (a fictional town) tested tap water at 10 homes. Each result below is in parts per billion (ppb) of lead. The current action level is 15 ppb, and it drops to 10 ppb in 2027.

Home	A	B	C	D	E	F	G	H	I	J
Lead (ppb)	2	4	5	8	9	11	13	16	19	28

How many of the 10 homes are above the current action level of 15 ppb?
What percent of the sampled homes are above 15 ppb?
How many homes would be above the 2027 action level of 10 ppb?
What percent of the sampled homes are above 10 ppb?
A system "exceeds" the action level when more than 10 percent of its samples are above it. Using your answer from item 2, does Brackham exceed the current 15 ppb action level? Explain with the percent.
Put the 10 results in order and find the median lead level.
Find the range of the 10 results.
Home J measured 28 ppb and has an old lead service line. Home A measured 2 ppb and has a copper line. Using these two results, explain why the pipe material matters.
Brackham has 4,000 homes but tested only 10. Give one reason those 10 homes might not fairly represent every home in town.
Suppose the town replaces the lead service lines at the three homes above 15 ppb, then tests those same homes again. Predict whether the percent above 15 ppb will rise, fall, or stay the same, and explain why.

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: 3 homes.
Homes H, I, and J measured 16, 19, and 28 ppb, which are the only results above 15 ppb.
Answer: 30 percent.
3 homes out of 10 is 3 divided by 10, which equals 0.30, or 30 percent.
Answer: 5 homes.
Homes F, G, H, I, and J measured 11, 13, 16, 19, and 28 ppb, all above 10 ppb.
Answer: 50 percent.
5 homes out of 10 is 5 divided by 10, which equals 0.50, or 50 percent.
Answer: Yes, it exceeds the action level.
30 percent of the homes are above 15 ppb, and 30 percent is greater than the 10 percent trigger, so the system exceeds the action level and must act.
Answer: 10 ppb.
In order the values are 2, 4, 5, 8, 9, 11, 13, 16, 19, 28. The two middle values are 9 and 11, and their average is (9 plus 11) divided by 2, which is 10 ppb.
Answer: 26 ppb.
The range is the largest minus the smallest: 28 minus 2 equals 26 ppb.
Answer: Lead pipes raise the lead level.
Home J with a lead service line measured far higher (28 ppb) than Home A with a copper line (2 ppb), showing that the lead service line added far more lead to the water than the copper line did; the small amount at Home A can come from solder or brass fixtures inside the house.
Answer: The sample may be too small or not random.
Ten homes out of 4,000 is a tiny share, and if those homes were chosen from only one neighborhood or only newer houses, they would miss homes with the oldest lead pipes, so the results might not match the whole town.
Answer: The percent above 15 ppb will likely fall.
Replacing the lead service lines at the three highest homes should lower their lead levels below 15 ppb, so fewer of the 10 homes would test above the action level, reducing the percent.

Differentiation

Support

Provide the 10 values already sorted from least to greatest so students can focus on counting, comparing to the action levels, and finding the median. Mark the 15 ppb and 10 ppb lines on the sorted list with a highlighter.

Extension

Ask students to design a fairer sampling plan for Brackham: how many homes they would test, how they would choose them, and why targeting homes known to have lead service lines is required under the real rule.

ELL supports

Pre-teach "action level," "service line," "median," and "range" with a labeled diagram of a house connected to a water main by a small pipe. Allow students to answer items 8, 9, and 10 with short phrases or a labeled sketch.