Lesson plan Grade 4 Math
Wardlow Reservoir's Hot Week: Water Lost to the Air
A grade 4 lesson on evaporation from a fictional reservoir, where students multiply daily losses across a week and round the totals for a town report.
Objectives
- Students will multiply a four-digit daily amount by a one-digit number of days.
- Students will round multi-digit totals to the nearest hundred and nearest thousand.
- Students will describe evaporation as water leaving a reservoir surface for the air.
Vocabulary
- Evaporation
- Evaporation happens when liquid water, often warmed by the sun, turns into an invisible gas called water vapor that rises into the air. It is how water leaves oceans, lakes, and puddles.
- Reservoir
- A human-made lake, usually created by a dam, that stores water for later. Reservoirs supply cities and farms and help control floods.
- Water cycle
- The water cycle is the continuous movement of water between the oceans, the air, and the land. The same water evaporates, forms clouds, falls as rain or snow, and flows back to the ocean before the process repeats.
Also: round, surface
Teacher overview
Wardlow is a fictional town whose drinking water sits in an open reservoir behind a low earthen dam. During a hot, dry week a measurable share of that stored water leaves the surface as vapor and never reaches a tap, and the town operators report the loss each Monday. This lesson uses that report to practice multiplying a daily amount across several days and rounding the totals for a public summary. Many students assume that water disappearing from a reservoir must be leaking out the bottom, so the hook is designed to make evaporation from an open surface visible before the arithmetic begins.
Procedure
Hook (5 min): Show the shallow pan of water you filled and left out a day or two before class, with the starting water line marked. Ask students where the missing water went and record their ideas without correcting them yet. Name evaporation and connect it to the reservoir at Wardlow, where the open surface loses water to the air on hot days.
Direct instruction (10 min): Explain that the Wardlow operators estimate the reservoir loses a set number of gallons to the air each hot day, and that the town wants a weekly figure. Model one example on the board that students will not repeat on the handout: a small pond that lost 900 gallons each day for 5 days lost 900 × 5 = 4,500 gallons. Show the partial products, since 9 hundreds × 5 is 45 hundreds. Then round 4,500 to the nearest thousand, landing on 5,000, and point out that the digit to the right of the thousands place decides the direction.
Guided practice and formative check (10 min): Give students whiteboards. Ask them to round 6,480 to the nearest thousand and hold up their boards. Look for 6,000. If fewer than four out of five students are correct, work through the place-value chart together before moving on, marking the thousands digit and the digit to its right. Repeat the check with 13,260 rounded to the nearest hundred, looking for 13,300.
Independent work (15 min): Distribute the student handout. Students complete all ten questions on their own, showing the partial products for the multiplication questions. Circulate and ask individual students to point to the digit that decided each rounding answer.
Close (5 min): Collect the handouts and ask two students to read their answers to questions 9 and 10 aloud. Close by asking the class why the town might print the rounded number in a newsletter while keeping the exact number in the operator log.
Student Handout
Wardlow Reservoir loses 1,250 gallons of water to the air each day during a hot week. How many gallons is that in 7 days?
Round your answer from question 1 to the nearest thousand gallons.
A smaller holding pond beside the reservoir loses 340 gallons each day. How many gallons does the pond lose in 7 days?
Add your answers from questions 1 and 3. How many gallons do the reservoir and the pond lose together in the week?
Round your answer from question 4 to the nearest hundred gallons.
Round your answer from question 4 to the nearest thousand gallons.
During a cooler week the reservoir loses 1,250 gallons a day on 3 hot days. How many gallons is that?
On the other 4 days of that cooler week the reservoir loses 610 gallons a day. How many gallons is that?
Add your answers from questions 7 and 8. How many gallons does the reservoir lose during the whole cooler week?
Round your answer from question 9 to the nearest thousand gallons.
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: 8,750 gallons.
1,250 × 7. Splitting 1,250 into 1,000 + 250 gives 1,000 × 7 = 7,000 and 250 × 7 = 1,750, and 7,000 + 1,750 = 8,750 gallons.Answer: 9,000 gallons.
The thousands digit is 8 and the digit to its right is 7, which is 5 or more, so the thousands digit goes up to 9.Answer: 2,380 gallons.
340 × 7. Splitting 340 into 300 + 40 gives 300 × 7 = 2,100 and 40 × 7 = 280, and 2,100 + 280 = 2,380 gallons.Answer: 11,130 gallons.
8,750 + 2,380 = 11,130 gallons. Adding the tens gives 50 + 80 = 130, so 100 regroups into the hundreds; the hundreds then total 700 + 300 + 100 = 1,100, and 1,000 of that regroups into the thousands place.Answer: 11,100 gallons.
The hundreds digit is 1 and the digit to its right is 3, which is less than 5, so the hundreds digit stays at 1.Answer: 11,000 gallons.
The thousands digit is 1 and the digit to its right is 1, which is less than 5, so the thousands digit stays and the rest become zeros.Answer: 3,750 gallons.
1,250 × 3. Splitting 1,250 into 1,000 + 250 gives 1,000 × 3 = 3,000 and 250 × 3 = 750, and 3,000 + 750 = 3,750 gallons.Answer: 2,440 gallons.
610 × 4. Splitting 610 into 600 + 10 gives 600 × 4 = 2,400 and 10 × 4 = 40, and 2,400 + 40 = 2,440 gallons.Answer: 6,190 gallons.
3,750 + 2,440 = 6,190 gallons for the whole cooler week.Answer: 6,000 gallons.
The thousands digit is 6 and the digit to its right is 1, which is less than 5, so the thousands digit stays at 6.
Differentiation
Support
Pair students who struggle with multi-digit multiplication and give them a partial-product organizer with the thousands, hundreds, and tens rows already labeled for questions 1, 3, 7, and 8. Provide a place-value chart with a highlighted column for each rounding question so the deciding digit is easy to locate.
Extension
Ask students to figure out how many days of loss at 1,250 gallons a day it would take to reach 20,000 gallons, and to justify the answer with multiplication rather than repeated addition.
ELL supports
Pre-teach "evaporation," "reservoir," "loses," and "round" with the pan demonstration and a labeled drawing showing arrows leaving the water surface. Provide the sentence frame: The reservoir loses ___ gallons each day, so in ___ days it loses ___ gallons.
Extensions
Have students refill the demonstration pan, mark the water line, and measure the drop after two school days, then compare a sunny windowsill with a shaded shelf and describe which pan lost more water.