Calculate Rectangle Area: 2½ m × 3¼ m Mixed Number Multiplication

Mixed Number Multiplication with Area Applications

What is the area of a rectangle with a length of 212 2\frac{1}{2} m and a width of314 3\frac{1}{4} m?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Let's find the area of the rectangle.
00:09 We'll use the formula: Area equals length times width.
00:14 Substitute the given side lengths into the formula.
00:19 First, convert any mixed fractions to improper fractions.
00:37 Multiply the numerators together, and then the denominators together.
00:44 Now, calculate the multiplication results.
00:53 Break the result into a whole number and a remainder.
01:04 Convert any remaining fraction into a whole or mixed number.
01:13 And that's how we solve this problem. Great job!

Step-by-step written solution

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1

Understand the problem

What is the area of a rectangle with a length of 212 2\frac{1}{2} m and a width of314 3\frac{1}{4} m?

2

Step-by-step solution

To find the area of a rectangle when given the dimensions as mixed numbers, follow these steps:

  • Step 1: Convert each mixed number to an improper fraction.
  • Step 2: Multiply the two fractions to find the area.
  • Step 3: Simplify the resulting fraction, if necessary, back to a mixed number.

Step 1: Convert the mixed numbers to improper fractions.

The length is 2122\frac{1}{2} meters. To convert 2122\frac{1}{2} to an improper fraction:

  • Multiply the whole number (2) by the denominator of the fractional part (2): 2×2=42 \times 2 = 4.
  • Add this result to the numerator of the fractional part (1): 4+1=54 + 1 = 5.
  • The improper fraction is 52\frac{5}{2}.

The width is 3143\frac{1}{4} meters. To convert 3143\frac{1}{4} to an improper fraction:

  • Multiply the whole number (3) by the denominator of the fractional part (4): 3×4=123 \times 4 = 12.
  • Add this result to the numerator of the fractional part (1): 12+1=1312 + 1 = 13.
  • The improper fraction is 134\frac{13}{4}.

Step 2: Multiply the two improper fractions.

Area=52×134=5×132×4=658\text{Area} = \frac{5}{2} \times \frac{13}{4} = \frac{5 \times 13}{2 \times 4} = \frac{65}{8}.

Step 3: Simplify 658\frac{65}{8} to a mixed number.

  • The quotient of 65÷865 \div 8 gives 8 as the whole number.
  • The remainder is 65(8×8)=6564=165 - (8 \times 8) = 65 - 64 = 1.
  • Thus, 658\frac{65}{8} converts to the mixed number 8188\frac{1}{8}.

Therefore, the area of the rectangle is 818\mathbf{8\frac{1}{8}} m².

3

Final Answer

818 8\frac{1}{8}

Key Points to Remember

Essential concepts to master this topic
  • Conversion Rule: Change mixed numbers to improper fractions before multiplying
  • Technique: For 212 2\frac{1}{2} , calculate (2×2) + 1 = 5, so 52 \frac{5}{2}
  • Check: Convert final answer back: 658=818 \frac{65}{8} = 8\frac{1}{8} since 65 ÷ 8 = 8 R1 ✓

Common Mistakes

Avoid these frequent errors
  • Adding mixed numbers instead of converting to improper fractions
    Don't add 2½ + 3¼ = 5¾ for area calculation! This gives you perimeter thinking, not area. Area requires multiplication, and mixed numbers must be converted to improper fractions first. Always convert to 52×134 \frac{5}{2} \times \frac{13}{4} before multiplying.

Practice Quiz

Test your knowledge with interactive questions

\( \frac{2}{3}\times\frac{5}{7}= \)

FAQ

Everything you need to know about this question

Why can't I just multiply the whole numbers and fractions separately?

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Multiplying 2 × 3 = 6 and ½ × ¼ = ⅛ separately gives you 6⅛, which is wrong! Mixed numbers represent combined values, so 2½ means 2 + ½, not separate parts to multiply individually.

How do I remember the formula for converting mixed numbers?

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Use this easy pattern: Multiply-Add-Keep! Multiply whole number by denominator, Add the numerator, Keep the same denominator. For 3¼: (3×4) + 1 = 13, so 134 \frac{13}{4} .

What if my final fraction doesn't convert to a mixed number evenly?

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That's normal! Not all answers are whole numbers. For 658 \frac{65}{8} , divide: 65 ÷ 8 = 8 remainder 1, so 818 8\frac{1}{8} . The remainder becomes your new numerator.

Can I use decimals instead of fractions?

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You can, but be careful with rounding! 212=2.5 2\frac{1}{2} = 2.5 and 314=3.25 3\frac{1}{4} = 3.25 , so 2.5 × 3.25 = 8.125. Converting back: 8.125 = 818 8\frac{1}{8} . Fractions are often more precise!

Why does the area come out as a mixed number when the dimensions are mixed numbers?

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When you multiply mixed numbers, the result can be any type of number! It depends on the specific values. Sometimes you get whole numbers, sometimes improper fractions, sometimes mixed numbers. Always simplify to the most appropriate form.

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