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Quiz & test questions Grade 7 Engineering & Design

Marlstone Treatment Pilot: A Grade 7 Engineering Unit Test

A 22-point grade 7 unit test with multiple-choice, short-answer, and computation items on design criteria, removal efficiency, and backwash waste.

Objectives

  1. Students will distinguish design criteria from design constraints in an engineering scenario.
  2. Students will calculate removal efficiency and backwash water waste using percent reasoning.

Vocabulary

Backwash
Backwash is when a treatment plant reverses the flow of water through a filter to flush out the dirt and particles it has trapped. It is like rinsing out a dirty sponge so the filter can keep working well.
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: criterion, constraint, removal efficiency

Teacher overview

This 30-minute unit test (22 points total) checks whether students can apply the engineering design process and percent reasoning to a fictional treatment pilot in the town of Marlstone. It mixes two multiple-choice items, one short-answer item, and four computation items, all built around the same pilot filter design and its performance data.

Marlstone Treatment Pilot: A Grade 7 Engineering Unit Test — Grade 7 Engineering & Design
Name: ____________________________ Date: ______________

Assessment

  1. (2 points) Which choice below is a design criterion for Marlstone's new filter, rather than a design constraint?

    • A) The filter must remove at least 90 percent of incoming sediment.
    • B) The filter must fit inside a 10-foot by 10-foot equipment room.
    • C) The filter must run on the plant's existing electrical supply.
    • D) The filter must be installed within six weeks.

  2. (4 points) A raw water sample entering Marlstone's pilot filter measures 8 NTU. After filtering, the sample measures 0.4 NTU. The removal-efficiency formula is Removal (%) = (influent − effluent) ÷ influent × 100. Use it to calculate the filter's percent removal.

  3. (4 points) A second pilot design reaches 99 percent removal efficiency. It treats the same 8 NTU raw water sample. Calculate this design's effluent turbidity, in NTU.

  4. (3 points) Real water treatment plants must keep finished-water turbidity at or below 0.3 NTU. They have to hit that mark in 95 percent of monthly samples. Look at the first pilot design's result in item 2. Does that design's filtered sample meet the 0.3 NTU target?

    • A) Yes, because 0.4 NTU is below the 0.3 NTU limit.
    • B) No, because 0.4 NTU is above the 0.3 NTU limit.
    • C) Yes, because the removal efficiency was above 90 percent.
    • D) There is not enough information to tell.

  5. (3 points) Marlstone's old filter wasted water as backwash equal to 20 percent of its total intake. A new design cuts that backwash waste to 8 percent of intake. The plant's intake is 5,000 gallons per day. How many fewer gallons of backwash water does the new design waste each day?

  6. (3 points) Now use your answer from item 5. How many fewer gallons of backwash water does the new design waste over a full 7-day week?

  7. (3 points) Short answer: Marlstone's town council also wants any new filter design to "avoid excessive water waste." In one or two sentences, explain why this goal is too vague to work as a design criterion. Then rewrite it as a criterion that is specific and measurable.

The quantities in this test describe a fictional design scenario.

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: A) The filter must remove at least 90 percent of incoming sediment. This is a criterion because it states a measurable target the design must achieve; the other three options are constraints, since each one limits the design instead of stating a performance goal.

  2. Answer: 95%. (8 − 0.4) ÷ 8 × 100 = 7.6 ÷ 8 × 100 = 95%.

  3. Answer: 0.08 NTU. At 99 percent removal, only 1 percent of the influent turbidity remains: 8 × (1 − 0.99) = 8 × 0.01 = 0.08 NTU.

  4. Answer: B) No, because 0.4 NTU is above the 0.3 NTU limit. The item 2 design's effluent of 0.4 NTU exceeds the regulatory target of 0.3 NTU, so it does not meet the standard even though its removal efficiency (95 percent) sounds high.

  5. Answer: 600 gallons fewer per day. Old backwash: 20% of 5,000 = 1,000 gallons/day. New backwash: 8% of 5,000 = 400 gallons/day. 1,000 − 400 = 600 gallons fewer per day.

  6. Answer: 4,200 gallons fewer per week. 600 gallons/day × 7 days = 4,200 gallons.

  7. Answer: Accept any explanation noting that "avoid excessive water waste" does not state a measurable target, so there is no way to test whether a design meets it. A specific, measurable rewrite might state: "the filter's backwash water use must not exceed 10 percent of total plant intake."

Differentiation

Support

For items 2, 3, 5, and 6, provide the formula or operation already set up with the known numbers filled in (for example, "(8 − 0.4) ÷ 8 × 100 = ___"), so students complete only the arithmetic. Allow a calculator for every computation item.

Extension

Ask students to calculate what influent turbidity, at a fixed 95 percent removal efficiency, would be needed to bring the effluent down to exactly 0.3 NTU, and to explain what that result suggests about the limits of a 95 percent removal design.

ELL supports

Provide a simple diagram showing water flowing through a filter, labeled "influent" on one side and "effluent" on the other, with the removal-efficiency formula written beside it. Allow item 7's rewritten criterion to be completed using a sentence frame: "The filter's backwash use must not go above ___ percent of intake."