Trapezoid Area Calculation: Finding Area with Heights 6cm and Parallel Sides 2.5cm and 4cm

Trapezoid Area Formula with Mixed Number Results

The trapezoid ABCD is shown below.

AB = 2.5 cm

DC = 4 cm

Height (h) = 6 cm

Calculate the area of the trapezoid.

2.52.52.5444h=6h=6h=6AAABBBCCCDDD

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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 We'll use the formula for calculating the area of a trapezoid
00:06 (Sum of bases(AB+DC) multiplied by height (H)) divided by 2
00:13 We'll substitute appropriate values and solve to find the area
00:21 6 divided by 2 becomes 3
00:26 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.

AB = 2.5 cm

DC = 4 cm

Height (h) = 6 cm

Calculate the area of the trapezoid.

2.52.52.5444h=6h=6h=6AAABBBCCCDDD

2

Step-by-step solution

First, let's remind ourselves of the formula for the area of a trapezoid:

A=(Base + Base) h2 A=\frac{\left(Base\text{ }+\text{ Base}\right)\text{ h}}{2}

We substitute the given values into the formula:

(2.5+4)*6 =
6.5*6=
39/2 =
19.5

3

Final Answer

1912 19\frac{1}{2}

Key Points to Remember

Essential concepts to master this topic
  • Formula: Area = (b1+b2)×h2 \frac{(b_1 + b_2) \times h}{2} where b₁, b₂ are parallel sides
  • Technique: Add parallel sides first: (2.5 + 4) × 6 ÷ 2 = 19.5
  • Check: Convert to mixed number: 39 ÷ 2 = 19½ cm² ✓

Common Mistakes

Avoid these frequent errors
  • Using non-parallel sides in the formula
    Don't use the slanted sides AD or BC in the area formula = completely wrong answer! Only the parallel sides (top and bottom) count as bases in a trapezoid. Always identify which sides are parallel before applying the formula.

Practice Quiz

Test your knowledge with interactive questions

Calculate the area of the trapezoid.

555141414666

FAQ

Everything you need to know about this question

Why do we only use the parallel sides in the formula?

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The trapezoid area formula is based on the average of the parallel sides times the height. The slanted sides don't affect the area - only the parallel bases and the perpendicular distance between them matter!

How do I know which sides are parallel?

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Look for sides that are horizontal or run in the same direction. In this problem, AB (top) = 2.5 cm and DC (bottom) = 4 cm are both horizontal, so they're parallel.

Can I leave my answer as a decimal instead of a mixed number?

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Yes! 19.5 cm² and 19½ cm² are exactly the same value. Choose whichever form the question asks for or feels more natural to you.

What if I forgot to divide by 2 at the end?

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You'd get 39 cm² instead of 19.5 cm² - exactly double the correct answer! The ÷2 step is crucial because the formula finds the average of the parallel sides first.

Does it matter which parallel side I call b₁ or b₂?

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Not at all! Since we're adding the parallel sides together, (2.5 + 4) gives the same result as (4 + 2.5). The order doesn't change the final area.

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