Adding Two to Three Digit Numbers

Addition with 3-digit numbers, Part 2 (with rounding)

A guided lesson for mathematics

Created and designed by Caulipower

First and second grade recommended

In this lesson, you will

• Add 3-digit numbers by 2-digit numbers with rounding

• Add 3-digit numbers by 3-digit numbers with rounding

• Take a quiz with two multiple choice questions and one essay

3-digit by 2-digit first!

I can write 237 words with my pencil before it breaks, and my little brother can write 58 words before his breaks. How many words can we write together before our pencils break?
First, let's think of what the number sentence will be. The number sentence is 237 + 58 = ? Then, we add the hundreds. Since there is only a hundredths place in the 237, the hundreds place is going to be 200. Next, we add the tens place. 30 + 50 is equal to 80, so our tens place is 80 for now, but when we add the ones place, the tens place will change. 7 + 8 = 15, but we can't put 15 in the ones place, because if we do, the number will be 2815, and that's not correct! We need to give the tens place the 10 in 15 so the 15 turnes into a "5" so the answer to the problem is 237 + 58 = 295!

3-digit by 3-digit next!

My cousin has 457 pokemon cards, while I only have 261 pokemon cards. How many pokemon cards do we have all together?

We always think about what the number sentence will look like first. The number sentence will look like 457 + 261 = ? Then we add the hundreds place. 400 + 200 = 600, so the hundreds place will be 600 for now. Next, we add the tens place. 50 + 60 is 110, but we can't put 110 in the tens place, so we give the 1 in the hundreds place of 110 to 600, so the new hundreds place is 700 and the tens place is a "1." Last, we add the ones and we have our answer. 7 + 1 = 8, so the ones place is an "8." Our answer is then 718.

Quiz time!

Time to show what you know!

Multiple Choice

What is 247 + 43?

• 380

• 280

• 290

• 390

Multiple Choice

What is 142 + 671?

• 713

• 700

• 831

• 813

Open Ended

What is the full answer to the problem on slide 4? (Feel free to go back!)

Thank you!

Created and designed by Caulipower