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Mental Math within 100
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What you will learn from this videoWhat you will learn
- How to do mental math with numbers up to 100.
- How we can use place value to add and subtract in our heads.
- Explore how doing mental math can help us build a tower, color a rainbow, and take care of mice!
- Discussion Questions
Before Video
What does mental math mean?ANSWERDoing math in your head without pencil and paper.
Using manipulatives, drawing, charts, and writing the numbers by lining them up by place value.
10 + 5 is easier to add because 10 is an easy number to use. To add, we just change the ones place.
A number that is easier to add or subtract with, like 10, 20, or 30. Skip counting means adding the same number over and over, which is also easier.
We can ask “5 plus what number is equal to 9?”
After Video
How can we use mental math to add 6 + 9?ANSWERWe can subtract one from 6 and add one to 9. Then we have 5 + 10. We can also first add 4 to 6, so that we have 10, and then we can add the remaining 5, so we have 10 + 5 = 15. There is more than one way.
Yes. We can count on from 17: 18, 19, 20. We counted 3 numbers, so 20 – 17 = 3.
We can first subtract 1 from 11 to make 10. Then subtract 3 more so we are subtracting 10 – 3, which is easier. We can also count on from 4 to 11.
The tens place changes but the ones place stays the same.
The tens place changes but the ones place stays the same.
- Vocabulary
- Add DEFINE
To put amounts together.
- Plus DEFINE
The word used to describe adding two amounts.
- Subtract DEFINE
To find the difference between two amounts.
- Minus DEFINE
The word used to describe subtracting two amounts.
- Mental Math DEFINE
Solving problems without paper and pencil.
- Friendly Numbers DEFINE
Numbers that are familiar and work as easy starting points, like 10 and 20.
- Skip Counting DEFINE
Counting by adding the same number over and over again.
- Add DEFINE
- Reading Material
- Practice Word Problems
- Practice Number Problems
- Lesson Plan
- Teacher Guide