Worksheet Grade 3 Math
Elmcross Reuse Center Log: A Grade 3 Add and Subtract Worksheet
A grade 3 worksheet where students add and subtract three-digit liter totals from a fictional town's water reuse log, then round to the nearest ten to check a sum.
Objectives
- Students will add and subtract three-digit numbers within 1000 using place value strategies.
- Students will round three-digit numbers to the nearest ten to estimate a sum.
- Students will explain why a rounded estimate can land on the same total as the exact sum.
Vocabulary
Key words: reuse, log, liter, round, estimate
Teacher overview
Towns that are short of water sometimes build a reuse center, a small plant that cleans the water from sinks and showers well enough to water parks and ball fields with it. Elmcross is a fictional town, and the daily liter totals in the log below were written for this worksheet rather than taken from a real reuse plant. Students add and subtract the daily totals, then round two of them to the nearest ten and compare the estimate with the exact sum. The error this worksheet is built to catch is the habit of lining up a two-digit number under a three-digit number by their first digits, as in item 7 (130 + 95), instead of by place value, which produces a sum that is badly off without looking obviously wrong to the student.
Student Worksheet
The town of Elmcross has a water reuse center. It cleans water from sinks and showers. That clean water is used on the town park. This log shows the liters the center cleaned each day.
| Day | Liters cleaned |
|---|---|
| Monday | 245 |
| Tuesday | 318 |
| Wednesday | 176 |
| Thursday | 209 |
| Friday | 152 |
- How many liters did the center clean on Monday and Tuesday?
- How many liters did the center clean on Wednesday and Thursday?
- How many more liters did the center clean on Tuesday than on Friday?
- How many fewer liters did the center clean on Wednesday than on Monday?
- The center cleaned 563 liters on Monday and Tuesday. It cleaned 176 more liters on Wednesday. How many liters is that in all?
- The park needs 400 liters. The center has 245 liters ready. How many more liters does the park need?
- On Saturday the center cleaned 130 liters. On Sunday it cleaned 95 liters. How many liters is that in all?
- Round the Tuesday total and the Friday total to the nearest ten. Then add the two rounded numbers.
- Now add the exact Tuesday total and the exact Friday total.
- Look at your answers to items 8 and 9. Explain why the two answers came out the way they did.
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: 563 liters.
Add 245 and 318 by place value: 200 + 300 = 500, 40 + 10 = 50, and 5 + 8 = 13, so 500 + 50 + 13 = 563 liters. - Answer: 385 liters.
Add 176 and 209: 100 + 200 = 300, 70 + 0 = 70, and 6 + 9 = 15, so 300 + 70 + 15 = 385 liters. - Answer: 166 liters.
Subtract 152 from 318. Take away 100 to reach 218, then 50 to reach 168, then 2 to reach 166 liters. - Answer: 69 liters.
Subtract 176 from 245. Take away 100 to reach 145, then 70 to reach 75, then 6 to reach 69 liters. - Answer: 739 liters.
Add 563 and 176: 500 + 100 = 600, 60 + 70 = 130, and 3 + 6 = 9, so 600 + 130 + 9 = 739 liters. - Answer: 155 liters.
Subtract 245 from 400. Take away 200 to reach 200, then 45 to reach 155 liters. - Answer: 225 liters.
Add 130 and 95: 130 + 90 = 220, and 220 + 5 = 225 liters. - Answer: 470 liters.
The Tuesday total 318 rounds to 320 because 318 is nearer to 320 than to 310, and the Friday total 152 rounds to 150 because 152 is nearer to 150 than to 160. Then 320 + 150 = 470 liters. - Answer: 470 liters.
Add the exact numbers: 300 + 100 = 400, 10 + 50 = 60, and 8 + 2 = 10, so 400 + 60 + 10 = 470 liters. - Answer: The two answers are the same.
Rounding moved the Tuesday total up by 2 and moved the Friday total down by 2, so the two changes cancelled each other and the estimate landed exactly on the true sum. Accept any explanation that names both the up-by-2 and the down-by-2 change.
Differentiation
Support
Provide a place-value chart with hundreds, tens, and ones columns for items 1 through 5, so students write each number in the correct column before adding. Give a labeled number line marked in tens from 300 to 330 and from 140 to 170 for item 8, so the rounding decision is a matter of marking a point. Allow base-ten blocks for the three subtraction items (3, 4, and 6).
Extension
Ask students to find the total the center cleaned across all five weekdays and check that total by adding the days in a different order. Have them choose two other days from the log, round both to the nearest ten, and decide before computing whether the estimate will be higher than, lower than, or equal to the exact sum, then prove it.
ELL supports
Pre-teach "reuse," "log," "cleaned," and "round" using a simple flow drawing of a sink, a small plant, and a park. Provide the sentence frames "The center cleaned ___ liters in all" and "___ rounds to ___ because it is nearer to ___." Let students point to the row of the log they are using before they start each item.