Quiz & test questions Grade 9 Math

Kestrel Bend Water Plant: A Grade 9 Treatment Math Quiz

A 30-point grade 9 quiz mixing multiple-choice, short-answer, and computation items on dosing, detention time, removal efficiency, and pressure at a fictional plant.

Grade: Grade 9
Subject: Math
Material: Quiz & test questions
Time: 35 min
Prep: No prep
Materials: Calculator

Standards

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Items 2, 3, 7, and 8 require students to carry milligrams per liter, million gallons per day, gallons, and psi through operator formulas, choosing and interpreting units consistently.

All materials for HSN-Q.A.1 →

HSA-CED.A.1 Common Core Math

Create equations and inequalities in one variable and use them to solve problems. Include equations arising from linear and quadratic functions, and simple rational and exponential functions.

How this material aligns: Item 9 has students write a one-variable feed equation from a fixed flow and solve it for the dose, the create-and-solve reasoning this standard names.

All materials for HSA-CED.A.1 →

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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 apply the pounds formula, detention time, and removal efficiency to plant data.
Students will convert between units and between feet of head and psi.

Vocabulary

Detention time: Detention time is how long water stays inside a tank or basin before flowing out. Water must stay long enough for each treatment step, like settling or disinfecting, to finish its job.
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: pounds formula, removal efficiency

Teacher overview

This 35-minute quiz is worth 30 points and checks whether students can apply core water-treatment math at a grade 9 level. It mixes multiple-choice, short-answer, and computation items built around one fictional plant, so students reuse the same flow across several formulas. The items cover the pounds formula, detention time, removal efficiency, a turbidity standard, and a pressure conversion, and they range from recall to multi-step application.

Kestrel Bend Water Plant: A Grade 9 Treatment Math Quiz — Grade 9 Math

Name: ____________________________ Date: ______________

Assessment

All items describe the Kestrel Bend Water Plant (a fictional plant), which treats 4.0 MGD (million gallons per day). Show your work on computation items.

(2 points) Which formula gives a chemical feed in pounds per day?
- A) dose (mg/L) x flow (MGD) x 8.34
- B) dose (mg/L) x flow (MGD) / 8.34
- C) dose (mg/L) + flow (MGD) x 8.34
- D) flow (MGD) x 8.34 / dose (mg/L)
(4 points) The plant doses chlorine at 2.5 mg/L. Find the chlorine feed in pounds per day at the plant's 4.0 MGD flow.
(3 points) A clarifier holds 240,000 gallons and receives the full 4.0 MGD. Find the detention time in hours. (Detention time = volume / flow.)
(3 points) Sedimentation basins are usually designed for 2 to 4 hours of detention. The detention time from item 3 is:
- A) within the typical range
- B) shorter than typical
- C) longer than typical
- D) exactly at the maximum
(4 points) The filters lower turbidity from an influent of 5.0 NTU to a finished 0.2 NTU. Find the removal efficiency as a percent. (Removal efficiency = (influent - effluent) / influent x 100.)
(2 points) The rule requires finished-water turbidity of 0.3 NTU or lower in 95 percent of samples. Does the 0.2 NTU finished value meet the rule? Answer yes or no and explain in one sentence.
(4 points) The Kestrel Bend tank holds its water surface 130 feet above a home. Find the pressure in psi at that home, using 1 foot of head = 0.433 psi.
(4 points) Convert the plant's 4.0 MGD flow to gallons per minute, using 1 MGD = 694 gpm.
(4 points) Write an equation for chlorine feed F (in lbs/day) as a function of dose D (in mg/L) at the plant's 4.0 MGD flow. Then find the dose that produces a feed of 100 lbs/day.

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: A) dose (mg/L) x flow (MGD) x 8.34. This is the pounds formula, which multiplies concentration, flow in MGD, and the constant 8.34 pounds per gallon.
Answer: 83.4 lbs/day. Feed = 2.5 mg/L x 4.0 MGD x 8.34 = 10 x 8.34 = 83.4 pounds per day.
Answer: 1.44 hours. Detention = 240,000 gallons / 4,000,000 gallons per day = 0.06 day; 0.06 x 24 = 1.44 hours.
Answer: B) shorter than typical. The 1.44-hour detention time is below the usual 2-to-4-hour design range for sedimentation.
Answer: 96 percent. (5.0 - 0.2) / 5.0 x 100 = 4.8 / 5.0 x 100 = 96 percent.
Answer: Yes. The finished value of 0.2 NTU is at or below the 0.3 NTU limit, so this sample meets the rule.
Answer: 56.3 psi. 130 feet x 0.433 psi per foot = 56.29, which rounds to 56.3 psi.
Answer: 2,776 gpm. 4.0 MGD x 694 gpm per MGD = 2,776 gallons per minute.
Answer: 3.0 mg/L. The equation is F = D x 4.0 x 8.34 = 33.36D. Set 33.36D = 100; D = 2.998, about 3.0 mg/L.

Differentiation

Support

Provide a formula card listing the pounds formula, detention time, removal efficiency, and the 0.433 psi-per-foot conversion, each with units labeled. Pre-fill the first multiplication step for item 2, and allow calculators on all computation items.

Extension

Ask students to find the clarifier volume, in gallons, that would give exactly 2 hours of detention at the plant's 4.0 MGD flow, working backward from the detention-time formula, and to state whether that is larger or smaller than the current 240,000-gallon clarifier.

ELL supports

Provide a labeled plant diagram (intake, clarifier, filters, tank) so item numbers map to a place students can see. Pre-teach "detention time," "removal efficiency," and "turbidity," and allow item 6 to be answered with a sentence frame: "The value of 0.2 NTU is ___ the 0.3 NTU limit, so it ___ the rule."