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Worksheet Grade 6 Math

Foxglove Meadows Lab Results: Percent of a Federal Standard

A grade 6 worksheet pairing fictional lead and chlorine lab readings with the real federal action level and disinfectant limit to practice percent-of-a-quantity problems.

Objectives

  1. Students will calculate what percent a measurement represents of a stated limit.
  2. Students will work backward from a percent to find the measurement it represents.
  3. Students will compare readings against real drinking-water regulatory limits.

Vocabulary

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.

Also: percent, residual, regulatory limit

Teacher overview

Foxglove Meadows Water District (a fictional water district) samples its distribution system for lead and chlorine several times a week. This worksheet pairs fictional lab readings with two real regulatory numbers: the current federal lead action level of 15 ppb and the maximum residual disinfectant level for chlorine of 4.0 mg/L. The lead action level is a trigger for utility action, not a safe level. EPA's health goal for lead is zero, and the action level drops to 10 ppb in 2027.

A common misconception in this kind of problem is treating the limit itself as the answer, rather than as the whole in a part-to-whole percent calculation. Problem 3 confronts this directly by asking students to find a measurement from a stated percent, reversing the usual direction of the calculation.

Foxglove Meadows Lab Results: Percent of a Federal Standard — Grade 6 Math
Name: ____________________________ Date: ______________

Student Worksheet

Foxglove Meadows Water District (fictional) tests its water for lead and chlorine every week. Use these facts for every problem. The current federal lead action level is 15 ppb. The chlorine limit, called the MRDL, is 4.0 mg/L.

  1. Monday's sample shows a lead reading of 3 ppb. What percent of the 15 ppb action level is that?

  2. Wednesday's sample shows a lead reading of 9 ppb. What percent of the action level is that?

  3. Friday's sample shows a lead reading that is 80 percent of the action level. What is Friday's reading, in ppb?

  4. Look at your answers to problems 1 through 3. Did the lead readings move toward the action level or away from it? Explain your answer.

  5. The chlorine reading on Monday is 1.2 mg/L. What percent of the 4.0 mg/L limit is that?

  6. The chlorine reading on Wednesday is 65 percent of the limit. What is Wednesday's reading, in mg/L?

  7. Foxglove Meadows sets its own safety buffer. No single reading should go above 90 percent of the limit. Does Wednesday's reading from problem 6 meet that rule? Use your percent to explain.

  8. A pipe repair plan aims to cut the average lead reading in half. The current average reading is 6 ppb. What will the new average be? What percent of the action level is that?

  9. Challenge. How many ppb equals 100 percent of the lead action level? Find how many ppb Monday's reading (problem 1) would need to rise to reach that amount. Then write that rise as a percent of Monday's original reading.

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

Answer Key

  1. Answer: 20 percent.
    3 ÷ 15 = 0.20, or 20 percent.

  2. Answer: 60 percent.
    9 ÷ 15 = 0.60, or 60 percent.

  3. Answer: 12 ppb.
    80 percent of 15 = 0.80 × 15 = 12.

  4. Answer: Toward the action level.
    Readings rose from 20 percent (3 ppb) on Monday to 60 percent (9 ppb) on Wednesday to 80 percent (12 ppb) on Friday, moving steadily closer to the 15 ppb action level across the week.

  5. Answer: 30 percent.
    1.2 ÷ 4.0 = 0.30, or 30 percent.

  6. Answer: 2.6 mg/L.
    65 percent of 4.0 = 0.65 × 4.0 = 2.6.

  7. Answer: Yes, it meets the buffer.
    2.6 ÷ 4.0 = 0.65, or 65 percent, which is below the 90 percent buffer threshold.

  8. Answer: 3 ppb, which is 20 percent of the action level.
    Half of 6 ppb is 3 ppb. 3 ÷ 15 = 0.20, or 20 percent.

  9. Answer: 12 ppb increase, which is 400 percent of Monday's original reading.
    100 percent of the action level is 15 ppb. Increasing from Monday's 3 ppb reading to 15 ppb is an increase of 15 − 3 = 12 ppb. As a percent of the original 3 ppb reading, 12 ÷ 3 = 4.00, or 400 percent.

Differentiation

Support (below grade level)

Provide a printed strip showing the two limits (15 ppb for lead, 4.0 mg/L for chlorine) alongside the percent formula "part ÷ whole × 100," and work problem 1 together as a class model before students attempt problems 2 and 3 independently.

Extension (above grade level)

Ask students to choose one percent, find the lead reading and the chlorine reading that would each sit at exactly that percent of their limits, then check that both fractions reduce to the same decimal.

ELL supports

Provide a simple two-column reference card pairing each vocabulary term ("action level," "residual," "buffer") with a one-sentence, plain-language definition and an icon. Allow the explanation in problem 4 to be answered with an arrow diagram (Monday → Wednesday → Friday with percents labeled) instead of full sentences.