Calculate Parallelogram Perimeter: Finding the Total Length of a 5.6 × 2.8 Shape

Q: Why do we multiply by 2 instead of adding all four sides?

Both methods give the same answer, but multiplying by 2 is faster and less error-prone! Since opposite sides of a parallelogram are equal, we have two pairs of identical sides: 5.6, 5.6, 2.8, 2.8.

Q: What if I forget which sides are equal?

In a parallelogram, opposite sides are always equal. So if one side is 5.6, the side across from it is also 5.6. Same for the 2.8 sides!

Q: Can I use this formula for rectangles too?

Yes! A rectangle is actually a special type of parallelogram, so $ P = 2(a + b) $ works perfectly for rectangles as well.

Q: What if I get a different decimal answer?

Double-check your addition: 5.6 + 2.8 = 8.4, then 2 × 8.4 = 16.8. Make sure to line up decimal points when adding and multiplying!

Parallelogram Perimeter with Decimal Dimensions

Calculate the perimeter of the following parallelogram:

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:07 Let's calculate the perimeter of the parallelogram.

00:10 Remember, in a parallelogram, opposite sides have the same length.

00:21 The perimeter is found by adding up the lengths of all four sides.

00:47 And that's how you find the perimeter! Great job!

Step-by-step written solution

Follow each step carefully to understand the complete solution

Understand the problem

Calculate the perimeter of the following parallelogram:

Step-by-step solution

To solve this problem, we apply the perimeter formula for parallelograms:

Step 1: Identify the lengths of sides $a$ and $b$ . The problem gives us $a = 5.6$ and $b = 2.8$ .
Step 2: Substitute these values into the formula $P = 2(a + b)$ .
Step 3: Calculate the result:
$a + b = 5.6 + 2.8 = 8.4$ .
$P = 2 \times 8.4 = 16.8$ .

Therefore, the perimeter of the parallelogram is $16.8$ .

Final Answer

16.8

Key Points to Remember

Essential concepts to master this topic

Formula: Perimeter equals 2(a + b) where a and b are adjacent sides
Technique: Add side lengths first: 5.6 + 2.8 = 8.4, then multiply by 2
Check: Count all four sides: 5.6 + 2.8 + 5.6 + 2.8 = 16.8 ✓

Common Mistakes

Avoid these frequent errors

Adding all four sides instead of using the doubling formula
Don't calculate 5.6 + 2.8 + 5.6 + 2.8 step by step = time-consuming and error-prone! Students often make arithmetic mistakes with repeated addition. Always use P = 2(a + b) to avoid calculation errors and work more efficiently.

Practice Quiz

Test your knowledge with interactive questions

Given the parallelogram:

Calculate the perimeter of the parallelogram.

FAQ

Everything you need to know about this question

Why do we multiply by 2 instead of adding all four sides?

Both methods give the same answer, but multiplying by 2 is faster and less error-prone! Since opposite sides of a parallelogram are equal, we have two pairs of identical sides: 5.6, 5.6, 2.8, 2.8.

What if I forget which sides are equal?

In a parallelogram, opposite sides are always equal. So if one side is 5.6, the side across from it is also 5.6. Same for the 2.8 sides!

Do I need to include units in my answer?

If the problem gives units (like cm or inches), include them in your answer. Since this problem shows 5.6 and 2.8 without units, your answer 16.8 is complete as is.

Can I use this formula for rectangles too?

Yes! A rectangle is actually a special type of parallelogram, so $P = 2(a + b)$ works perfectly for rectangles as well.

What if I get a different decimal answer?

Double-check your addition: 5.6 + 2.8 = 8.4, then 2 × 8.4 = 16.8. Make sure to line up decimal points when adding and multiplying!

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