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The areas of two mathematically similar shapes are in the ratio 
49:81
The length of the smaller shape is 
24.5cm
Work out the length of the larger shape.

The areas of two mathematically similar shapes are in the ratio 49:8149:81. The length of the smaller shape is 24.5cm24.5\,\text{cm}. Work out the length of the larger shape.

Full solution

Q. The areas of two mathematically similar shapes are in the ratio 49:8149:81. The length of the smaller shape is 24.5cm24.5\,\text{cm}. Work out the length of the larger shape.
  1. Understand Relationship: Understand the relationship between the areas of similar shapes and their corresponding lengths.\newlineThe ratio of the areas of similar shapes is equal to the square of the ratio of their corresponding lengths. This means that if the areas are in the ratio 49:8149:81, then the lengths are in the ratio 49:81\sqrt{49}:\sqrt{81}, which simplifies to 7:97:9.
  2. Calculate Length of Larger Shape: Calculate the length of the larger shape using the ratio of lengths.\newlineWe know the length of the smaller shape is 24.5cm24.5\,\text{cm}, which corresponds to the smaller number in the ratio of lengths (77). To find the length of the larger shape, we set up a proportion:\newlinesmaller lengthlarger length=smaller ratio numberlarger ratio number\frac{\text{smaller length}}{\text{larger length}} = \frac{\text{smaller ratio number}}{\text{larger ratio number}}\newline24.5cmlarger length=79\frac{24.5\,\text{cm}}{\text{larger length}} = \frac{7}{9}
  3. Solve Proportion: Solve the proportion for the length of the larger shape.\newline(larger length)=24.5cm×97(\text{larger length}) = \frac{24.5 \, \text{cm} \times 9}{7}\newline(larger length)=220.5cm7(\text{larger length}) = \frac{220.5 \, \text{cm}}{7}\newline(larger length)=31.5cm(\text{larger length}) = 31.5 \, \text{cm}

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