Revisiting Addition and Subtraction

A Lesson for Third Graders

by Suzy Ronfeldt

Students benefit from repeated practice with addition and subtraction throughout the year. In her book, Third-Grade Math: A Month-to-Month Guide (Math Solutions Publications, 2003), Suzy Ronfeldt provides a midyear perspective on providing practice, suggesting fresh approaches to computing with larger numbers that are suitable for older students as well. The problems are useful not only for your students’ learning but also for assessing their progress.

How Old Is the Coin?

Children can find many opportunities to figure out the age of something—whether it’s a coin in their money bags or a character in a book. For example, have students examine quarters and determine the years in which they were minted. For a quarter minted in 1974, for example, have them first estimate the coin’s age. Then give them quiet time to figure out the solution step-by-step on paper. Next, either in pairs or in a class discussion, ask students to share their strategies. (See Figure 1.)

Figure 1. Marcus figured out the age of a dime that was minted in 1966.

Homework Extensions

• Children find three different coins and record the name and value of each coin and its mint date. Then they figure out the age of the coin today and explain their reasoning.
• Students look for the oldest U.S. coin they can find. They then figure out the age of the coin, showing their work and explaining their reasoning.

How Old Is the Character?

When you and the children read books together, you’ll find many opportunities to figure out how old a character might be. For example, in the book Ramona the Pest, by Beverly Cleary (New York: William Morrow), Ramona is in kindergarten, which makes her about five years old. According to the copyright date, the book was written in 1968. How old would Ramona be today? (See Figure 2.)

 

Figure 2. Nan calculated Ramona the Pest’s age in 2001.

How Long Ago?

Checking the copyright dates of books you read in the classroom provides plenty of opportunities to ask “How long ago?” questions. For instance, Caps for Sale, by Esphyr Slobodkina (New York: W.R. Scott), was written in 1940. Ask your students to figure out how long ago 1940 was. (See Figure 3.)

 

Figure 3. Kihyun calculated that in 2003, the year 1940 was 63 years ago.

Also, in my class, I meet individually with four children each day to discuss the books they are reading as part of their weekly homework. When you have one-on-one book conferences with students, along with discussing their reading, ask how long ago their books were published.

School Days Problems

Here are three school days problems for your students to solve:

1. How many school days are there in a school year? (Make calendars available for students to solve this problem.)
2. How many days has school been in session this year so far?
3. How many school days are left in the school year?

 

Calendar Days So Far

At the bottom of CNN’s television picture, the scrolling words often include information on the number of days in the calendar year so far. You can use this information from time to time to pose problems for your students. For example:

1. What day of the year is today?
2. December 31 is the 365th day (or 366th day in leap years). How many days are left until the end of the year?

Pages Left to Read in a Book

After you and your students have read some pages in a chapter of a book, ask them to figure out how many pages are left to read. This is also a good question to ask children during one-on-one book conferences.

 

From Online Newsletter Issue Number 13, Spring 2004

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Related Publication:
A Month-to-Month Guide: Third-Grade Math
by Suzy Ronfeldt