Multiplying fractions and mixed numbers
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लेसन नोट्स
What is Multiplication?
- Multiplication is a quick way to add the same number many times. For example, 3 × 4 means 4 + 4 + 4 = 12.
- The numbers you multiply are called factors. The answer is called the product.
- The multiplication sign is × (like 3 × 4) or a dot (like 3 ⋅ 4). Both mean the same.
- Multiplication is commutative: 3 × 4 = 4 × 3. The order does not change the product.
- You can think of multiplication as counting objects in a rectangle. If a rectangle is 3 rows and 4 columns, it has 3 × 4 = 12 squares.
Multiplying a Fraction by a Whole Number
- To multiply a fraction by a whole number, multiply the top number (the numerator) by the whole number. The bottom number (the denominator) stays the same.
- Example: \frac{2}{5} \times 3 = \frac{2 \times 3}{5} = \frac{6}{5}.
- If the product is an improper fraction (top bigger than bottom), you can write it as a mixed number: \frac{6}{5} = 1\frac{1}{5}.
- Think of \frac{2}{5} \times 3 as 3 groups of \frac{2}{5}, which is \frac{2}{5} + \frac{2}{5} + \frac{2}{5} = \frac{6}{5}.
Multiplying a Fraction by a Fraction
- To multiply two fractions, multiply the numerators together and multiply the denominators together.
- Example: \frac{2}{3} \times \frac{4}{5} = \frac{2 \times 4}{3 \times 5} = \frac{8}{15}.
- You can simplify before multiplying if you see a common factor. For example, \frac{2}{3} \times \frac{3}{4} can be simplified to \frac{1}{1} \times \frac{1}{2} = \frac{1}{2}.
- Always check if your answer can be simplified. For example, \frac{4}{8} simplifies to \frac{1}{2}.
Why Multiplying by a Fraction Less Than 1 Makes the Answer Smaller
- When you multiply a number by a fraction that is less than 1, the product is smaller than the original number.
- Example: 6 \times \frac{1}{2} = 3. The answer 3 is less than 6.
- This is because multiplying by \frac{1}{2} is like finding half of the number.
- Multiplying by \frac{3}{4} is like finding three quarters of the number, so the answer is less than the number.
- This is different from multiplying by a whole number greater than 1, which makes the answer bigger.
Using Area Models for Fraction Multiplication
- An area model is a rectangle divided into equal parts. It helps you see fraction multiplication.
- To multiply \frac{1}{2} \times \frac{1}{3}, draw a rectangle, split it into 2 rows and 3 columns. Shade 1 row and 1 column. The overlapping part is \frac{1}{6} of the whole.
- The area of a rectangle is length × width. If the sides are fractions, the area is the product of those fractions.
- Area models show why \frac{2}{3} \times \frac{3}{4} = \frac{6}{12} = \frac{1}{2}.
Multiplying Mixed Numbers
- A mixed number has a whole number and a fraction, like 2\frac{1}{3}.
- To multiply mixed numbers, first change them to improper fractions (where the numerator is bigger than the denominator).
- To change 2\frac{1}{3} to an improper fraction: multiply the whole number by the denominator (2 × 3 = 6), add the numerator (6 + 1 = 7), and keep the denominator: \frac{7}{3}.
- Then multiply the improper fractions as usual.
- Example: 1\frac{1}{2} \times 2\frac{1}{3} = \frac{3}{2} \times \frac{7}{3} = \frac{21}{6} = 3\frac{1}{2}.
Dividing with Fractions (Unit Fractions)
- A unit fraction has 1 as the numerator, like \frac{1}{2}, \frac{1}{3}, \frac{1}{4}.
- To divide a whole number by a unit fraction, multiply by the denominator. Example: 4 \div \frac{1}{2} = 4 \times 2 = 8.
- To divide a unit fraction by a whole number, multiply the denominator by the whole number. Example: \frac{1}{3} \div 2 = \frac{1}{3 \times 2} = \frac{1}{6}.
- Division is the opposite of multiplication. If 3 \times 4 = 12, then 12 \div 3 = 4.
Solving Real-World Problems
- You can use fraction multiplication to find a fraction of an amount. For example, \frac{2}{3} of 12 is \frac{2}{3} \times 12 = 8.
- If a recipe needs \frac{3}{4} cup of sugar and you make half the recipe, you need \frac{3}{4} \times \frac{1}{2} = \frac{3}{8} cup.
- If you run \frac{2}{5} of a 10 km race, you run \frac{2}{5} \times 10 = 4 km.
- When solving word problems, look for words like 'of', 'times', or 'product' to know you need to multiply.
Key Vocabulary
- Fraction: a number that shows part of a whole, like \frac{1}{2}.
- Numerator: the top number of a fraction. It tells how many parts you have.
- Denominator: the bottom number of a fraction. It tells how many equal parts the whole is divided into.
- Improper fraction: a fraction where the numerator is bigger than or equal to the denominator, like \frac{7}{3}.
- Mixed number: a whole number plus a fraction, like 2\frac{1}{3}.
- Product: the answer you get when you multiply.
- Unit fraction: a fraction with numerator 1, like \frac{1}{5}.
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प्रैक्टिस सवाल
फ्री प्रीव्यू — 62 में से 8 सवाल। सभी देखने के लिए साइन अप करें।
1.What is the result of a multiplication operation called?
Easy- Asum
- Bdifference
- Cproduct
- Dquotient
2.Which symbol is commonly used to denote multiplication?
Easy- A+
- B×
- C−
- D÷
3.Multiplying a fraction less than 1 by a whole number always gives a smaller answer than the whole number.
EasyTrue or false?
4.Which expression gives the same value as 5 × 2/3?
Medium- A10/3
- B5/6
- C2/15
- D7/3
5.Which of the following are correct ways to write 2 times 3? (select all that apply)
Medium- A2×3
- B2⋅3
- C2+3
- D23
- E2×3
6.Match each multiplication expression with its product.
Medium- 1/2 × 1/3
- 2/5 × 3/4
- 3 × 2/9
- 1/6
- 3/10
- 2/3
7.Arrange these steps in the correct order to multiply 1 1/2 by 3.
Medium- Convert 1 1/2 to an improper fraction: 3/2
- Multiply 3/2 by 3 to get 9/2
- Write the answer as a mixed number: 4 1/2
8.A rectangle has a length of 2/3 meter and a width of 3/4 meter. What is its area?
Medium- A1/2 square meter
- B5/7 square meter
- C6/12 square meter
- D1/2 meter
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