Calculate Dimensions: Finding Lengths of a 750 m² Plot from a 20×25 m² Similar Plot

Similar Figures with Area Scaling

Imagine two similar plots of land.

The first plot is 20×25 m², while the area of the second plot is 750 750 m².

Calculate the lengths of the secod plot of land.

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Found the dimensions of the second area
00:03 Find the area of the square
00:07 Multiply side by side and solve to find the area
00:16 Calculate the ratio of areas
00:22 Factor with factor (250) and reduce
00:29 This is the ratio of areas
00:36 Find the similarity ratio
00:41 The similarity ratio equals the square root of the area ratio
00:46 Isolate X
00:55 This is the value of X
00:59 Now let's find the second side
01:04 Use the formula to calculate square area
01:07 Side multiplied by side
01:11 Substitute appropriate values and solve for Y
01:14 Isolate Y
01:19 Divide 750 by 10
01:26 Factor square root of 6 into factors (square root of 3) and (square root of 2)
01:37 Factor 3 into two square root of 3 and reduce
01:53 Multiply numerator and denominator by square root of 2
02:05 And this is the solution to the problem

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Imagine two similar plots of land.

The first plot is 20×25 m², while the area of the second plot is 750 750 m².

Calculate the lengths of the secod plot of land.

2

Step-by-step solution

Let's solve the problem by using the relationship between similar figures.

The area of the first plot is 20×25=500m2 20 \times 25 = 500 \, \text{m}^2 . The area of the second plot is given as 750m2 750 \, \text{m}^2 .

We use the property of similar figures where the ratio of their areas is the square of the ratio of their corresponding lengths.

Let the ratio of similarity (scale factor) be k k , so:

(500750)=k2 \left(\frac{500}{750}\right) = k^2

Simplified, this becomes:

k2=23 k^2 = \frac{2}{3}

Taking the square root of both sides:

k=23 k = \sqrt{\frac{2}{3}}

To find the dimensions of the second plot, multiply the dimensions of the first plot by k1 k^{-1} (as the second plot is larger, we use reciprocal since direct k k reduces dimensions):

The first plot dimensions are 20 m and 25 m. Applying the scale factor:

  • Length 1 of second plot = 20(32)=2032=106 20 \cdot \left(\sqrt{\frac{3}{2}}\right) = 20\sqrt{\frac{3}{2}} = 10\sqrt{6}
  • Length 2 of second plot = 25(32)=2532=2562 25 \cdot \left(\sqrt{\frac{3}{2}}\right) = 25\sqrt{\frac{3}{2}} = \frac{25\sqrt{6}}{2}

Hence, the dimensions of the second plot are 106×2562 10\sqrt{6} \times \frac{25\sqrt{6}}{2} .

This matches option 3.

Therefore, the calculated lengths of the second plot of land are 106m 10\sqrt{6} \, \text{m} and 2562m \frac{25\sqrt{6}}{2} \, \text{m} .

3

Final Answer

106×2562 10\sqrt{6}×\frac{25\sqrt{6}}{2}

Key Points to Remember

Essential concepts to master this topic
  • Area Ratio Rule: Area ratio equals square of length ratio
  • Scale Factor: k=750500=32 k = \sqrt{\frac{750}{500}} = \sqrt{\frac{3}{2}} for enlargement
  • Verification: Check 106×2562=750 10\sqrt{6} \times \frac{25\sqrt{6}}{2} = 750 m² ✓

Common Mistakes

Avoid these frequent errors
  • Using area ratio directly as length ratio
    Don't multiply dimensions by 750500=1.5 \frac{750}{500} = 1.5 directly = wrong dimensions! Area scales by the square of the length ratio, not the ratio itself. Always take the square root of the area ratio to find the length scale factor.

Practice Quiz

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FAQ

Everything you need to know about this question

Why do I need to take the square root of the area ratio?

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Because area is a two-dimensional measurement! When you scale a rectangle by factor k, both length and width are multiplied by k, so area is multiplied by k2 k^2 . To find k from areas, use k=new areaold area k = \sqrt{\frac{\text{new area}}{\text{old area}}} .

How do I know which plot is being scaled up or down?

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Compare the areas! Since 750 m² > 500 m², the second plot is larger. This means we're scaling up, so our scale factor 32 \sqrt{\frac{3}{2}} is greater than 1.

Why are the final dimensions in radical form?

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Because 32 \sqrt{\frac{3}{2}} doesn't simplify to a nice decimal! Mathematical answers are often more exact when left as radicals rather than rounded decimals.

Can I check my answer without complex calculations?

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Yes! Multiply your dimensions: 106×2562=250×62=750 10\sqrt{6} \times \frac{25\sqrt{6}}{2} = \frac{250 \times 6}{2} = 750 m². If this equals the given area, you're correct!

What if the areas were reversed in the problem?

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Then you'd be scaling down! Your scale factor would be 500750=23 \sqrt{\frac{500}{750}} = \sqrt{\frac{2}{3}} , which is less than 1, making smaller dimensions.

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