Adding and Subtracting Multiples of 10 (within 100)

Free sample questions, a clear explanation, and 5 practice skills with an AI tutor that guides without giving the answer away.

Super Stacks of Ten!

Have you ever built a tall tower with LEGO bricks? Imagine each LEGO brick is a yummy cookie. It's hard to count a giant pile of cookies one by one! But what if we stack them into towers of 10? Suddenly, counting becomes super easy! Adding and subtracting big numbers like 20, 30, or 70 is just like playing with these neat stacks of ten. Let's become masters of the tens!

From Blocks to Drawings (Concrete & Pictorial)

In class, we used special blocks called "ten rods." Each rod is a stack of 10 ones. When we want to add 20 + 30, it's like taking 2 ten rods and 3 ten rods and pushing them together. How many rods do you have now? Five! That's 5 tens, which is 50!

We don't always have blocks, but we can always draw them! A simple rectangle can be our ten rod. To solve 60 - 20, you can:

Draw 6 rectangles (to show 60).
Cross out 2 of them (to take away 20).
Count how many are left. Four! That's 4 tens, or 40!

⭐ Key Takeaway! ⭐

Adding and subtracting tens is just like adding and subtracting smaller numbers! For 40 + 50, just think 4 + 5 = 9. Then, add a zero to make it 90! It's a super-secret math trick!

Let's Solve a Puzzle! (Abstract)

Now, let's use our big brains to solve a problem without any blocks or drawings.

Leo has a sticker book. He has 40 shiny star stickers. His friend gives him 30 more for his birthday! How many stickers does Leo have in all?

4 tens + 3 tens = 7 tens. So, 40 + 30 = 70 stickers! Wow!

You did an amazing job working with these big numbers today. Keep practicing, and soon you'll be an expert at adding and subtracting stacks of ten!

Sample questions

1. Mia has 2 ten-rods. Her friend gives her 3 more ten-rods. How many small cubes does Mia have in all?

○ 5 cubes

○ 23 cubes

✓ 50 cubes

○ 55 cubes

Answer: 50 cubes — Count the total number of ten-rods. Each ten-rod is 10 small cubes. How many tens do you have?

2. You have 4 bundles of 10 pencils. You get 2 more bundles of 10 pencils. How many pencils do you have in total?

○ 6 pencils

○ 42 pencils

○ 4020 pencils

✓ 60 pencils

Answer: 60 pencils — Count how many bundles of ten pencils you have altogether. Then count by tens.

3. There is 1 ten-block and 6 ten-blocks. How many units are there in total?

○ 7 units

✓ 70 units

○ 16 units

○ 1060 units

Answer: 70 units — Think: 1 ten and 6 tens make how many tens? What number is that?

Skills in this topic

Add multiples of 10 (e.g., 20 + 30) using concrete objects (e.g., ten rods).
Subtract multiples of 10 (e.g., 50 - 20) using concrete objects.
Represent addition and subtraction of multiples of 10 using pictorial models (e.g., drawing ten rods).
Solve addition and subtraction problems involving multiples of 10 within 100 abstractly.
Create a real-world problem that requires adding or subtracting multiples of 10 (e.g., counting groups of 10 items).

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