By Fatskills Exam Guides Team — the exam nerds behind 28,500+ quizzes and 2.1M practice questions across 500+ global exams.
By the end of this topic, students will be able to: - Add and subtract 2-digit numbers using mental and written methods. - Use number lines and counting blocks to support calculations. - Apply addition and subtraction facts to solve simple problems. - Demonstrate an understanding of the concept of place value in 2-digit numbers. - Begin to develop fluency with basic addition and subtraction facts within 20.
In this topic, students will learn about the basic concepts of addition and subtraction with 2-digit numbers. They will understand that a 2-digit number is made up of a tens digit and a ones digit. For example, the number 45 is made up of 4 tens and 5 ones.
When adding or subtracting 2-digit numbers, students will need to consider the place value of each digit. For example, when adding 45 and 27, students will need to add the tens digits (4 + 2 = 6) and then add the ones digits (5 + 7 = 12).
Students will also learn how to use number lines and counting blocks to support their calculations. A number line is a visual representation of numbers in order, and counting blocks are physical blocks that can be used to represent numbers. For example, a student might use counting blocks to represent the number 45 by using 4 tens blocks and 5 ones blocks.
Sarah has 45 pencils in her pencil case. Her friend gives her 27 more pencils. How many pencils does Sarah have now?
Let's use counting blocks to help us solve this problem. We can represent the number 45 by using 4 tens blocks and 5 ones blocks. We can then add 27 more pencils by using 2 tens blocks and 7 ones blocks.
Now, let's count the total number of pencils. We can start by counting the tens blocks: 4 + 2 = 6. Then, we can count the ones blocks: 5 + 7 = 12. So, Sarah now has 6 tens blocks and 12 ones blocks, which is equal to 67 pencils.
Tom has 75 marbles in his jar. He gives 27 marbles to his brother. How many marbles does Tom have left?
Let's use a number line to help us solve this problem. We can start at the number 75 and count back 27 numbers. We can use counting blocks to help us count: 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45.
We can see that Tom has 48 marbles left.
One common misconception is that students think that when adding or subtracting 2-digit numbers, they need to add or subtract the numbers in the ones place first and then add or subtract the numbers in the tens place. For example, when adding 45 and 27, students might think that they need to add 5 + 7 = 12 and then add 4 + 2 = 6. However, this is incorrect, and students need to add the tens digits first and then add the ones digits.
Another common misconception is that students think that when subtracting 2-digit numbers, they need to count back the same number of units as the number being subtracted. For example, when subtracting 27 from 75, students might think that they need to count back 27 units. However, this is incorrect, and students need to count back the correct number of units based on the place value of the digits.
When answering addition and subtraction questions with 2-digit numbers, students should make sure to:
What is the result of adding 45 and 27?
A) 72 B) 67 C) 74 D) 85
Correct answer: B) 67
Why the distractors fail:
What is the result of subtracting 27 from 75?
A) 48 B) 62 C) 85 D) 92
Correct answer: A) 48
What is the result of adding 25 and 15?
A) 40 B) 45 C) 50 D) 60
Correct answer: B) 40
What is the result of subtracting 35 from 67?
A) 32 B) 42 C) 52 D) 62
Correct answer: A) 32
What is the result of adding 45 and 10?
A) 55 B) 65 C) 75 D) 85
Correct answer: B) 55
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