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Classroom activity Grade 3 Math

Fernpath Waterworks Meter Match: A Grade 3 Subtraction Game

Partners take the roles of meter reader and checker on a fictional utility route, subtracting meter readings within 1000 and checking each answer by adding it back.

Objectives

  1. Students will subtract meter readings within 1000 to find one month of water use.
  2. Students will check a subtraction by adding the difference back to the earlier reading.
  3. Students will compare eight three-digit differences to find the greatest one.

Vocabulary

Water meter
A device that measures how much water a home or business uses so the utility can bill fairly. Reading the meter can also reveal hidden leaks.

Also: meter reading, difference, regroup

Teacher overview

Meter Match is a partner game for pairs in which one student plays the meter reader and the other plays the checker on a route belonging to Fernpath Waterworks, a fictional utility. A house meter never resets, so it shows the running total of every gallon that has ever passed through it, and the gallons used in one month are the difference between two readings. That running total is the source of the misconception the game targets: students read 612 on the dial and record 612 gallons of monthly use, when the house actually used the 105 gallons between last month's reading and this month's. The checker role exists to catch that error, because adding the difference back to the earlier reading has to land exactly on the later reading. A real household uses thousands of gallons in a month, so the readings in this game are kept under 1000 to fit grade 3 subtraction, and it is worth telling students that real monthly amounts are much larger.

Activity Directions

  1. Setup (5 min). Seat students in pairs and give each pair one printed route sheet and a cup of about 20 counters. Both partners keep the route sheet where they can see it. Explain that the sheet lists eight houses, and that each house shows the reading taken last month and the reading taken this month.
  2. Model one house (5 min). Using House 1 from the sheet, show the class that the meter went from 214 gallons to 386 gallons. Subtract on the board to find 172 gallons of use, then add 172 back to 214 to land on 386 and explain that this is how a checker proves the answer.
  3. Assign roles (2 min). In each pair, one partner is the meter reader for the odd-numbered houses and the other is the meter reader for the even-numbered houses. The partner who is not reading is the checker for that round.
  4. Play the rounds (18 min). For each house in order, the reader writes the subtraction and finds the gallons used, then the checker adds that answer back to the earlier reading. If the sum matches the later reading, the pair takes one counter and moves on. If it does not match, both partners rework the house together before taking any counter. Play ends when all eight houses are finished, so a pair that works carefully can earn eight counters.
  5. Record and compare (7 min). Partners complete items 9, 10, and 11 on the route sheet, then trade sheets with a neighboring pair and compare answers for any house where the two pairs disagree.
  6. Debrief (3 min). Ask two questions and take answers from several pairs: how the checking step told a pair that an answer was wrong, and why a meter that reads 612 gallons does not mean the house used 612 gallons this month. Close by asking where else a running total shows up, such as a car odometer.
Fernpath Waterworks Meter Match: A Grade 3 Subtraction Game — Grade 3 Math
Name: ____________________________ Date: ______________

Student Handout

Fernpath Waterworks reads the water meter at each house once a month. A meter counts every gallon the house has ever used, so it never goes back to zero. The gallons used in one month are the difference between the two readings.

House Reading last month Reading this month
House 1 214 gallons 386 gallons
House 2 375 gallons 540 gallons
House 3 418 gallons 703 gallons
House 4 638 gallons 925 gallons
House 5 96 gallons 480 gallons
House 6 507 gallons 612 gallons
House 7 275 gallons 850 gallons
House 8 444 gallons 999 gallons
  1. How many gallons did House 1 use this month?
  2. How many gallons did House 2 use this month?
  3. How many gallons did House 3 use this month?
  4. How many gallons did House 4 use this month?
  5. How many gallons did House 5 use this month?
  6. How many gallons did House 6 use this month?
  7. How many gallons did House 7 use this month?
  8. How many gallons did House 8 use this month?
  9. Look at your answers for items 1 through 8. What is the greatest number of gallons any one house used?
  10. Add the gallons used by House 1 and the gallons used by House 2. How many gallons is that?
  11. Toby says House 6 used 612 gallons because 612 is the number on the meter this month. House 6 read 507 gallons last month. How many gallons did House 6 really use?

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: 172 gallons. Subtract the earlier reading from the later one: 386 − 214 = 172 gallons. Check: 172 + 214 = 386.
  2. Answer: 165 gallons. 540 − 375 = 165 gallons. Check: 165 + 375 = 540.
  3. Answer: 285 gallons. 703 − 418 = 285 gallons, with regrouping in both the tens and the hundreds. Check: 285 + 418 = 703.
  4. Answer: 287 gallons. 925 − 638 = 287 gallons. Check: 287 + 638 = 925.
  5. Answer: 384 gallons. 480 − 96 = 384 gallons. Check: 384 + 96 = 480.
  6. Answer: 105 gallons. 612 − 507 = 105 gallons. Check: 105 + 507 = 612.
  7. Answer: 575 gallons. 850 − 275 = 575 gallons. Check: 575 + 275 = 850.
  8. Answer: 555 gallons. 999 − 444 = 555 gallons, which needs no regrouping. Check: 555 + 444 = 999.
  9. Answer: 575 gallons. House 7 used 575 gallons, which is more than 172, 165, 285, 287, 384, 105, and 555 gallons.
  10. Answer: 337 gallons. House 1 used 172 gallons and House 2 used 165 gallons, so 172 + 165 = 337 gallons.
  11. Answer: 105 gallons. The 612 on the meter counts every gallon the house has ever used. This month's use is the difference between the two readings, so 612 − 507 = 105 gallons.

Differentiation

Support

Give this group a route sheet with the first four houses only, printed in a place-value grid so the hundreds, tens, and ones line up without extra effort. Provide base ten blocks for the three houses that need regrouping twice (Houses 2, 3, and 4), and let the teacher or an aide serve as the checker for the first two rounds. Students who finish the four houses may take the remaining four as a challenge.

Extension

Ask pairs to write two new house cards of their own, choosing readings under 1000 that force regrouping in both the tens and the hundreds place, then trade cards with another pair and play two more rounds. Have them also find the total gallons used by all eight houses on the printed route and explain the order they added in.

ELL supports

Pre-teach "meter," "reading," "route," "last month," and "this month" with a photograph of a house water meter and a two-column chart showing the two readings side by side. Post the sentence frame "House ___ used ___ gallons this month." Allow the checker to show agreement with a thumbs up rather than an explanation, and pair newcomers with a partner who can restate item 11 in simpler words.

Extensions

Have students read the school's water meter or a classroom rain gauge on the same day each week for a month and record the running total each time. Ask them to find the use for each week by subtracting one reading from the previous one, then discuss why the differences change from week to week while the meter number only grows.