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Lesson plan Grade 5 Math

Fernbrook Pool's Showerheads: A Grade 5 Fraction Multiplication Lesson

A grade 5 lesson where students multiply fractions to find a reduced showerhead flow rate, then scale it by whole numbers to find a fictional pool's daily water savings.

Objectives

  1. Students will multiply a mixed number by a fraction to find a reduced water-flow rate.
  2. Students will multiply a flow rate by whole numbers of minutes and fixtures to find total water use.
  3. Students will compare two flow rates to calculate a daily water savings.

Vocabulary

Flow rate
Flow rate measures how much water moves past a point in a certain amount of time, like gallons per minute through a garden hose. Bigger pipes and stronger pushes give bigger flow rates.

Also: fraction, mixed number, gallons per minute, conservation

Teacher overview

Fernbrook Community Pool, a fictional pool used for this lesson, is deciding whether to replace the eight showerheads in its locker room with WaterSense-labeled models. A standard showerhead flows at 2 1/2 gallons per minute, while a WaterSense model uses only four-fifths as much water per minute. This lesson has students multiply that fraction against the standard rate to find the new rate, then scale the result by whole numbers of minutes and fixtures to see how much water the switch would save in a single day. A common misconception in this lesson is that "using four-fifths as much" means subtracting 4/5 from the rate instead of multiplying by it; the direct instruction step addresses that error by modeling 5/2 x 4/5 = 2 and showing that subtracting 4/5 would give 1 7/10 instead.

Procedure

Hook (5 min): Show two labeled cards, "Standard: 2 1/2 gallons per minute" and "WaterSense: ? gallons per minute," and tell students that the WaterSense showerhead uses four-fifths as much water per minute as the standard one. Ask students to estimate whether the missing number is closer to 1, 2, or 2 1/2.

Direct instruction (10 min): Model multiplying the mixed number by the fraction: 2 1/2 = 5/2, so 5/2 x 4/5 = 20/10 = 2. Confirm that the WaterSense showerhead's rate is 2 gallons per minute, matching the real WaterSense standard. Then point out that subtracting instead, 2 1/2 - 4/5 = 1 7/10, does not find four-fifths of the rate.

Guided practice (15 min): In pairs, students calculate how much water one showerhead of each type uses during a 5-minute shower: standard is 2 1/2 x 5 = 12 1/2 gallons, and WaterSense is 2 x 5 = 10 gallons. Students then subtract to find the savings from one shower: 12 1/2 - 10 = 2 1/2 gallons.

Independent practice (15 min): Each student answers two numbered questions on the handout, using the pool's eight showerheads, each used once per day for 5 minutes:

  1. How many total gallons would the eight standard showerheads use in one day?
  2. How many total gallons would the eight WaterSense showerheads use in one day, and how many gallons less is that than the standard total?

Closure / exit ticket (5 min): Students answer question 3 on an index card. Collect and scan for correct multiplication of the daily savings by 6 before dismissal.

  1. If the pool uses its showers 6 days a week, how many gallons would switching to WaterSense save in one week?

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: 100 gal.
    One standard showerhead uses 12 1/2 gallons for a 5-minute shower (2 1/2 x 5). Eight showerheads use 12 1/2 x 8 = 100 gallons total.
  2. Answer: 80 gal; 20 gal less.
    One WaterSense showerhead uses 2 x 5 = 10 gallons for a 5-minute shower. Eight showerheads use 10 x 8 = 80 gallons total. 100 - 80 = 20 gallons less than the standard total.
  3. Answer: 120 gal.
    For the exit ticket, the daily savings of 20 gallons, multiplied by 6 days a week, equals 120 gallons saved in one week.

Differentiation

Support (below grade level)

Provide the fraction multiplication 5/2 x 4/5 already set up with the numerators and denominators labeled, so students only need to multiply across and simplify, and allow a calculator to convert fractions to decimals for the multi-step gallon calculations.

Extension (above grade level)

Ask students to find what fraction of the standard flow rate a showerhead using exactly 1 1/2 gallons per minute represents (1 1/2 divided by 2 1/2), and explain what that fraction means in terms of water saved compared to the WaterSense rate used in the lesson.

ELL supports

Pre-teach "flow rate," "standard," and "savings" with a simple diagram of two showerheads of different sizes above matching measuring cups. Provide a sentence frame for independent practice: "The eight ___ showerheads use ___ gallons in one day."

Extensions

Have students check how many showerheads their own school building has and, using the same fraction and rates from this lesson, calculate how many gallons a full switch to WaterSense fixtures could save the school in a week of daily use.