Calculate Trapezoid Area: ABCD with Bases 10cm, 7cm and Height 5cm

Trapezoid Area with Parallel Base Formula

The trapezoid ABCD is shown below.

The base AB is equal to 10 cm.

The base DC is equal to 7 cm.

The height of ABCD is 5 cm.

Calculate the area of the trapezoid ABCD.

101010777555AAABBBCCCDDDEEE

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Calculate the area of the trapezoid
00:03 Let's use the formula for calculating the area of a trapezoid
00:07 ((sum of bases) multiplied by height) divided by 2
00:16 Let's substitute appropriate values according to the given data and solve for the area
00:56 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

The trapezoid ABCD is shown below.

The base AB is equal to 10 cm.

The base DC is equal to 7 cm.

The height of ABCD is 5 cm.

Calculate the area of the trapezoid ABCD.

101010777555AAABBBCCCDDDEEE

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the given information.
  • Step 2: Apply the appropriate formula for the area of a trapezoid.
  • Step 3: Perform the necessary calculations to find the area.

Now, let's work through each step:

Step 1: We are given that the bases of the trapezoid AB=10cm AB = 10 \, \text{cm} and DC=7cm DC = 7 \, \text{cm} , and the height of the trapezoid is 5cm 5 \, \text{cm} .

Step 2: The formula for finding the area of a trapezoid is: Area=12×(Base1+Base2)×Height \text{Area} = \frac{1}{2} \times (\text{Base}_1 + \text{Base}_2) \times \text{Height}

Step 3: Substituting the known values into the formula, we have: Area=12×(10+7)×5 \text{Area} = \frac{1}{2} \times (10 + 7) \times 5

Simplifying inside the parentheses and calculating, we get: Area=12×17×5=12×85=42.5 \text{Area} = \frac{1}{2} \times 17 \times 5 = \frac{1}{2} \times 85 = 42.5

Therefore, the area of trapezoid ABCD is 42.5\textbf{42.5} square centimeters.

Thus, the correct choice from the provided options is 42.5.

3

Final Answer

42.5

Key Points to Remember

Essential concepts to master this topic
  • Formula: Area = 12×(Base1+Base2)×Height \frac{1}{2} \times (\text{Base}_1 + \text{Base}_2) \times \text{Height}
  • Technique: Add bases first: 10 + 7 = 17, then multiply by height and divide by 2
  • Check: Verify units are consistent and result makes sense: 42.5 cm² ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to divide by 2 in the area formula
    Don't just multiply (base₁ + base₂) × height = 17 × 5 = 85! This gives double the actual area because you're calculating a rectangle instead of a trapezoid. Always divide by 2 to get the correct trapezoid area.

Practice Quiz

Test your knowledge with interactive questions

Given the following trapezoid:

AAABBBCCCDDD584

Calculate the area of the trapezoid ABCD.

FAQ

Everything you need to know about this question

Why do we divide by 2 in the trapezoid formula?

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A trapezoid is like half of a parallelogram. When you add the two bases and multiply by height, you're finding the area of a rectangle. Dividing by 2 gives you the actual trapezoid area!

Does it matter which base I call base₁ or base₂?

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No, it doesn't matter! Since we're adding the bases together (10 + 7 = 17), the order doesn't change the final answer. You'll get 42.5 cm² either way.

How do I identify the height in a trapezoid diagram?

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The height is always the perpendicular distance between the two parallel bases. Look for the line that forms a 90° angle with both bases - that's your height!

What if the trapezoid looks tilted or rotated?

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The formula works the same way! The height is still perpendicular to the parallel bases, even if the trapezoid is drawn at an angle. Just identify the two parallel sides and the perpendicular distance between them.

Can I use this formula for any quadrilateral?

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No! This formula only works for trapezoids because they have exactly two parallel sides. For other quadrilaterals, you need different formulas or break them into triangles.

What units should my answer have?

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Since you're multiplying length × length, your answer will be in square units (cm², m², etc.). Always include the correct area units in your final answer!

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