Multiplication:
Multiplication is a mathematical operation that involves adding a number to itself several times. For example, 3×43 \times 43×4 means adding 3 four times (3 + 3 + 3 + 3). Fluently multiplying within 100 means quickly and accurately multiplying numbers where the product is 100 or less, using strategies that help solve these problems efficiently.
Strategies for Multiplying Within 100:
- Using Known Multiplication Facts: memorize multiplication tables to recall answers quickly.
- Skip Counting: Repeat the count by a number to reach the product (e.g., for 3×4, count "3, 6, 9, 12").
- Using the Distributive Property: Break down larger problems into smaller parts (e.g., 6×8 as 6×5+6×3).
- Commutative Property of Multiplication: Recognize that the order of factors doesn’t matter (3×4=4×3).
- Using Arrays: Visualizes multiplication by arranging objects in rows and columns.
Example 1:
Simple Multiplication Using Skip Counting. Find the product of 4×5.
Solution Using Skip Counting:
- Count by 4 five times: 4, 8, 12, 16, 20.
- Final solution: 4×5=20
Example 2:
Using the Distributive Property: Find 6×8 by breaking it down.
Solution Using Distributive Property:
- Break down 8 as 5 + 3.
- Rewrite 6×8 as 6×(5+3).
- Use the distributive property: 6×5+6×3.
- Add the two results: 30 + 18 = 48.
- Final solution: 30+18=48.
Example 3:
Memorizing a One-Digit Product: What is 9×7?
Solution using memorization:
- Recall from memory or previous practice that 9×7=63.
- Final solution: 9×7=63.
Example 4: 2-Digit by 1-Digit Multiplication Using Standard Algorithm Calculate 9×23.
Solution:
- Write the numbers vertically and multiply each place separately
23
× 9
-----
- Multiply the ones place:
- 9×3=27. Write down 7 in the one's place and carry over 2 to the tens.
- Multiply the tens place:
- 9×2=18.
- Add the carried-over 2: 18 + 2 = 20.
- Write the final product:
23
× 9
-----
207
Final solution: 9×23 = 207.
Example 4:
Multiplying two 2-digit numbers: calculate 13×15.
Solution Using the Distributive Property:
- Break down both numbers:
- Apply the distributive property:
- 13×15=(10+3)×(10+5).
- Distribute each term:
- 10×10=100
- 10×5=50
- 3×10=30
- 3×5=15
- Add the products together:
Final solution: 13×15=195.
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