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Three solid shapes A, B and C are similar - Edexcel - GCSE Maths - Question 16 - 2018 - Paper 1

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Three solid shapes A, B and C are similar. The surface area of shape A is 4 cm² The surface area of shape B is 25 cm² The ratio of the volume of shape B to the vol... show full transcript

Worked Solution & Example Answer:Three solid shapes A, B and C are similar - Edexcel - GCSE Maths - Question 16 - 2018 - Paper 1

Step 1

Find the ratio of lengths for shapes A and B

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Answer

To find the ratio of lengths we use the relationship between surface area and lengths in similar shapes. The surface area ratio is given by:

Surface Area of ASurface Area of B=425\frac{Surface \ Area \ of \ A}{Surface \ Area \ of \ B} = \frac{4}{25}

The ratio of surface areas is proportional to the square of the ratio of corresponding lengths. Therefore, if the ratio of lengths is ( k ), we have:

425=k2\frac{4}{25} = k^2

Solving for k gives:

k=425=25k = \sqrt{\frac{4}{25}} = \frac{2}{5}

Step 2

Find the ratio of lengths for shapes B and C

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Answer

Given the volume ratio of shape B to shape C as 27:64, we can derive the ratio of lengths. The volume ratio is proportional to the cube of the ratio of corresponding lengths. If the ratio of lengths is ( m ), we have:

Volume of BVolume of C=2764=m3\frac{Volume \ of \ B}{Volume \ of \ C} = \frac{27}{64} = m^3

Thus, solving for m gives:

m=27643=34m = \sqrt[3]{\frac{27}{64}} = \frac{3}{4}

Step 3

Find the ratio of height of shape A to height of shape C

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Answer

Finally, the ratio of the height of shape A to the height of shape C can be derived by using the ratios we found. We know:

  • The ratio of lengths A to B is ( \frac{2}{5} )
  • The ratio of lengths B to C is ( \frac{3}{4} )

To find the ratio A to C, we multiply the ratios:

Height of AHeight of C=Height of AHeight of B×Height of BHeight of C=25×34=620=310\frac{Height \ of \ A}{Height \ of \ C} = \frac{Height \ of \ A}{Height \ of \ B} \times \frac{Height \ of \ B}{Height \ of \ C} = \frac{2}{5} \times \frac{3}{4} = \frac{6}{20} = \frac{3}{10}

Thus, the ratio of the height of shape A to the height of shape C is ( \frac{3}{10} ).

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