Article
Jeff Foott/Minden Pictures
Math,

Very Busy Beavers

Scientists are bringing these big rodents back to streams where they once lived 

By Mara Grunbaum
From the September 2021 Issue

Learning Objective: Students will use regrouping to subtract multidigit numbers related to beavers and their habitats.

Lexile: 780L; 540L
Focus Area: Numbers and Operations,
Standards
  • CCSS: 3.NBT.A.2, MP5, MP6, MP7 TEKS: 3.4A

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Lexile® measure

  • 780L
  • 540L

As you read, think about what tarantula pet owners could do to protect wild tarantulas.

As you read, think about what tarantula pet owners could do to protect wild tarantulas.

Mike Sevigny hikes to a muddy pond near Seattle, Washington. He knows a beaver made it. His job is to bring the beaver to a place where it can be more helpful. 

Sevigny is the wildlife manager for the Tulalip Tribes, a group of Native American tribes in Washington. Since 2014, his team has captured about 300 beavers and moved them to different streams. It’s part of an effort to restore wetlands in the area.  

Mike Sevigny hikes to a pond. The pond is muddy. The pond is near Seattle, Washington. A beaver made the pond. Sevigny knows that. It is Sevigny’s job to bring the beaver to a different place. Sevigny will bring the beaver to a place where it can be helpful.

Sevigny is a wildlife manager. He works for the Tulalip Tribes. The Tulalip Tribes is a group of Native American tribes. The tribes live in Washington State. Sevigny’s team has captured about 300 beavers since 2014. The team moved the beavers to different streams. The team moves beavers to help restore wetlands in Washington. 

Courtesy of Mike Sevigny 

Mike Sevigny 

Beavers are the largest rodents in North America. They can weigh as much as a golden retriever! Beavers use long, curved teeth to gnaw on trees. They build dams across streams using sticks and mud. Over time, water builds up to form a pond. The pond provides a home for beavers and other animals.

The beaver pond helps the environment too. The dam filters out pollution, making the stream cleaner. Slowing the water flow reduces the risk of flooding when it rains. 

Beavers are the largest rodents in North America. They can weigh as much as a golden retriever! Beavers have long teeth. Beaver teeth are curved. Beavers use their teeth to gnaw on trees. Beavers build dams across streams. Beavers build using sticks and mud. Water builds up around the sticks and mud. The water forms a pond. The pond provides a home for beavers and other animals.

The beaver pond helps the environment too. The beaver dam filters out pollution. That makes the stream cleaner. The beaver dam makes the water flow slower. Slower water is less likely to cause a flood when it rains.

Living With Beavers

Beavers once lived all over North America. By 1900, millions of beavers had been killed. Today, many people are trying to bring beavers back to their old habitats. 

But sometimes beavers build dams where people don’t want them. That’s when scientists like Sevigny step in.

Beavers used to live in many places in North America. Humans had killed millions of beavers by the year 1900. Many people today are trying to bring beavers back to their old habitats.

Sometimes beavers build dams where people don’t want the beavers to build them. That's when scientists like Sevigny step in.

Jeff Foott/Minden Pictures

Scientists release a beaver to a new home.

Caring for nature is part of the Tulalip Tribes’ heritage. Sevigny’s team traps beavers and releases them in streams where the animals haven’t lived in a long time. 

Soon the area transforms. “They’re incredible critters, and they work for free,” says Sevigny.

Caring for nature is part of the Tulalip Tribes' heritage. Sevigny’s team traps beavers.  The team releases the beavers in streams where beavers haven’t lived in a long time.

Soon the area changes. “They’re incredible critters. They work for free,” says Sevigny.

MATH TALK

What things can you measure to study beavers’ impact on a stream? 

MATH TALK

What things can you measure to study beavers’ impact on a stream? 

Subtraction

What to Do

What to Do When you subtract, sometimes the digit in one place value column is larger than the digit you’re trying to take away from. In this case, you can regroup, or exchange, numbers without changing their value. Try it with place value blocks!

Example

Scientists in Washington relocated 84 beavers in 2017. In 2018, they moved 56 fewer beavers. How many beavers did they relocate in 2018?

• You can’t subtract 6 from 4 in the ones place. So regroup one of the tens from 84 by exchanging it for 10 ones.

• Cross out 5 groups of ten and 6 ones.

• Determine what’s left. There are 2 tens and 8 ones, or 28 remaining.

So scientists relocated 28 beavers in 2018.

Subtraction

What to Do

What to Do When you subtract, sometimes the digit in one place value column is larger than the digit you’re trying to take away from. In this case, you can regroup, or exchange, numbers without changing their value. Try it with place value blocks!

Example

Scientists in Washington relocated 84 beavers in 2017. In 2018, they moved 56 fewer beavers. How many beavers did they relocate in 2018?

• You can’t subtract 6 from 4 in the ones place. So regroup one of the tens from 84 by exchanging it for 10 ones.

• Cross out 5 groups of ten and 6 ones.

• Determine what’s left. There are 2 tens and 8 ones, or 28 remaining.

So scientists relocated 28 beavers in 2018.

Now You Try It

Use a separate piece of paper to answer the questions, modeling each problem with place value blocks or discs. Mark your final answers below.

Use a separate piece of paper to answer the questions, modeling each problem with place value blocks or discs. Mark your final answers below.

American beavers can grow up to 51 inches long. Their tails make up 12 inches of that length. How long can beavers be, not including the length of their tails? 

American beavers can grow up to 51 inches long. Their tails make up 12 inches of that length. How long can beavers be, not including the length of their tails? 

The pandemic made it harder for Washington scientists to relocate beavers. In 2020, they moved 19 beavers. In 2016, they moved 83. How many fewer beavers did they relocate in 2020?

The pandemic made it harder for Washington scientists to relocate beavers. In 2020, they moved 19 beavers. In 2016, they moved 83. How many fewer beavers did they relocate in 2020?

Scientists in Utah counted baby salmon in parts of a stream with and without a beaver pond. There were 405 baby salmon in one area near the pond. There were 195 baby salmon in a similar area far from the pond. How many more baby salmon lived near the beaver pond?

Scientists in Utah counted baby salmon in parts of a stream with and without a beaver pond. There were 405 baby salmon in one area near the pond. There were 195 baby salmon in a similar area far from the pond. How many more baby salmon lived near the beaver pond?

Scientists in Wyoming measured forested areas alongside streams. These forests averaged 111 feet wide along streams with beaver ponds. They were 35 feet wide along streams with no beavers. How much wider were the forests around the streams with beavers? 

Scientists in Wyoming measured forested areas alongside streams. These forests averaged 111 feet wide along streams with beaver ponds. They were 35 feet wide along streams with no beavers. How much wider were the forests around the streams with beavers? 

Continue the Learning Journey

  • Rewatch the video “Animals Can Build It!”. Then use the information you learned from both the video and the article to create a pamphlet explaining the importance of beavers. Include at least 3 number facts in your pamphlet.
  • Practice subtraction using household items. Use long items, such as pencils, to represent your tens. Use short items, such as paperclips, to represent your ones. For example, you would model 68 using 6 pencils and 8 paperclips. Ask a family member to choose 2 numbers between 10 and 100. Then model subtracting the smaller number from the larger number using your chosen objects. Don’t forget to exchange 1 long item for 10 short items if you need to regroup!

Continue the Learning Journey

  • Rewatch the video “Animals Can Build It!”. Then use the information you learned from both the video and the article to create a pamphlet explaining the importance of beavers. Include at least 3 number facts in your pamphlet.
  • Practice subtraction using household items. Use long items, such as pencils, to represent your tens. Use short items, such as paperclips, to represent your ones. For example, you would model 68 using 6 pencils and 8 paperclips. Ask a family member to choose 2 numbers between 10 and 100. Then model subtracting the smaller number from the larger number using your chosen objects. Don’t forget to exchange 1 long item for 10 short items if you need to regroup!
video (2)
video (2)
Activities (2)
Question & Answer Sheets
Skills Activities
Answer Key (1)
Step-by-Step Lesson Plan
Download the Lesson Plan

1. SPARK ENGAGEMENT.

Play the video “Animals Can Build It!” Then, before or after reading the article, spark a discussion based on the following questions:

  • What is an example of an animal or insect that may be considered a pest but is also helpful to our environment?  
  • How many hours in a day do you think beavers spend building dams? Explain your reasoning. 

2. INTRODUCE THE MATH CONCEPT AND VOCABULARY.

  • Which value is greater, 13 dimes or $1? Explain. (13 dimes is the greater value because 10 dimes is equivalent to $1. 13 dimes is equivalent to $1.30, which is greater than $1.) 
  • How many pennies are equivalent to $1? (100 pennies) 
  • When working with whole numbers, we can also regroup, or exchange, a number without changing its value.  
  • What is the value of 1 ten and 3 ones? (13) How could I regroup 13 to represent only the ones place value? (Exchange 1 ten for 10 ones and combine it with the 3 ones to make 13 ones.) 
  • We can use regrouping to help us subtract numbers. Play the math video “Subtraction Strategies.”

3. WORK THROUGH THE “WHAT TO DO” BOX.

  • Look at the number you are subtracting from. What happened to the digit 8 in the tens place? (It was regrouped and changed to 7 tens. The 1 ten was exchanged for 10 ones and added to the 4 in the ones place.) 
  • How many ones are there now? (14 ones) Can you subtract 6 ones from 14 ones? (Yes, because 14 is greater than 6.)  
  • Can you subtract 5 tens from 7 tens? (Yes, because 70 is greater than 50.) 
  • What do the remaining place value blocks represent? (28) 28 is the difference between 84 and 56.  
  • Will you always have to regroup when subtracting numbers? Explain. (No; answers will vary.)

4. REINFORCE WITH MATH PRACTICE. 

Have students complete problems 1 through 4 on page 7. 

TEACHER’S TIP:

Encourage students to write out numbers in expanded form when subtracting. This will help them line up their numbers and see how much is being regrouped from one place value to the next.  − Victoria J. Dixon, TX

TEACHER’S TIP:

Encourage students to write out numbers in expanded form when subtracting. This will help them line up their numbers and see how much is being regrouped from one place value to the next.  − Victoria J. Dixon, TX

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