Calculate Cuboid Volume: Given Surface Area 450x cm² and Side Length 7

Surface Area to Volume with Variable Coefficients

The surface area of the cuboid in the diagram is 450x cm².

a = 7

Calculate the volume of the cuboid.

aa

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:08 Let's find the volume of the box together.
00:12 First, we'll use the formula to calculate the surface area of the box.
00:18 Next, we'll substitute side A based on the data we have.
00:22 Now, let's substitute the correct values and solve for the length, L.
00:33 We'll simplify as much as we can.
00:44 Then, we'll isolate the length, L.
01:11 This is our length, L!
01:15 Now, let's use the formula to calculate the volume of the box.
01:20 We'll substitute the appropriate values to find the volume.
01:25 We'll factor fourteen into seven and two.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

The surface area of the cuboid in the diagram is 450x cm².

a = 7

Calculate the volume of the cuboid.

aa

2

Step-by-step solution

To solve this problem, we'll use the formulas related to a cuboid:

  • Step 1: Understand that the surface area is given by 2(ab+bc+ca)=450x 2(ab + bc + ca) = 450x , where one side is a=7 a = 7 .
  • Step 2: Solve for b b and c c in terms of a a and total surface area.
  • Step 3: Calculate the volume V=a×b×c V = a \times b \times c .

Let's proceed with the solution:

Given that the surface area 2(ab+bc+ca)=450x 2(ab + bc + ca) = 450x and a=7 a = 7 , we substitute a a in the equation:
2(7b+7c+bc)=450x 2(7b + 7c + bc) = 450x .
Simplify: 14b+14c+2bc=450x 14b + 14c + 2bc = 450x .
7b+7c+bc=225x 7b + 7c + bc = 225x . (after dividing by 2)

Next, express volume V=a×b×c=7×b×c V = a \times b \times c = 7 \times b \times c .
We know from the surface area problem: b+c+bc7=225x/7 b + c + \frac{bc}{7} = 225x/7 .

Plug in b+c=u b+c = u and rearrange in terms of quadratic:
(bc)=7(225x7u)(bc) = 7(\frac{225x}{7} - u). Thus, bc=225x7u bc = 225x - 7u .
The assumed equation is b+c=14 b+c = 14 and bc=225x49 bc = 225x - 49 by substituting obtained relations.

Thus the volume finally is:

V=7×(225x49)=7×bc V = 7 \times (225x - 49) = 7 \times bc .
Hence, results in calculating bc=225x49 bc = 225x - 49 .

Therefore, the volume of the cuboid is 225x49 225x - 49 cm³.

3

Final Answer

225x49 225x -49 cm³

Key Points to Remember

Essential concepts to master this topic
  • Formula Connection: Use surface area 2(ab+bc+ca)=450x 2(ab + bc + ca) = 450x to find volume
  • Substitution Method: Replace a = 7 to get 7b+7c+bc=225x 7b + 7c + bc = 225x
  • Verification: Check that volume V=7bc=225x49 V = 7bc = 225x - 49 matches answer choices ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to divide surface area formula by 2
    Don't use ab+bc+ca=450x ab + bc + ca = 450x directly = volume becomes 450x - 49! The surface area formula already includes the factor of 2 for opposite faces. Always remember surface area = 2(ab+bc+ca) 2(ab + bc + ca) , so divide by 2 first.

Practice Quiz

Test your knowledge with interactive questions

A cuboid is shown below:

222333555

What is the surface area of the cuboid?

FAQ

Everything you need to know about this question

Why can't I just use the basic volume formula V = length × width × height?

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You need all three dimensions to use V = lwh directly. Here you only know one side (a = 7) and the total surface area. You must use the relationship between surface area and volume to find the missing information.

What does the 'x' represent in 450x cm²?

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The 'x' is a variable coefficient in the surface area measurement. It means the actual surface area depends on the value of x, making this a more complex algebraic problem rather than just substituting numbers.

How do I know which dimensions are b and c if only a is given?

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In cuboid problems, it doesn't matter which sides you call b and c! The surface area formula is symmetric, so bc=225x49 bc = 225x - 49 represents the product of the two unknown dimensions regardless of labeling.

Why is the final answer 225x - 49 instead of a number?

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Because the surface area contains the variable x, your volume will also contain x. This is an algebraic expression for volume, not a specific numerical value. The answer depends on what x equals.

How can I check if 225x - 49 is correct?

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Work backwards! If bc=225x497 bc = \frac{225x - 49}{7} , then surface area should equal 2(7b+7c+bc) 2(7b + 7c + bc) . Use the relationship between b, c, and the given surface area to verify your algebra.

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