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Mathematics: Post your doubts here!

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http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Mathematics (0580)/0580_w13_qp_21.pdf
how do I solve question 11? i tried cross multiplication but the answer doesnt match the mark scheme.

First of all look at the units. The model is in cm^3 while the full size is in m^3. Convert the cm^3 into m^3.

1 cm = 0.01 m
1 cm^3 = (0.01)^3 = 0.000001 m^3

1200 cm^3 = 1200 x 0.000001 m^3
1200 cm^3 = 0.0012 m^3

Now apply the similarity ratios. Since we're dealing with volume, the ratio should be cubed.

We know the ratio is 1 : n , so we can write it in the form 1 / n.

1 / n = volume of model / volume of the full sized plane

Since we're dealing with volume, the ratio should be cubed.

1^3 / n^3 = 0.0012 / 4050

0.0012 n^3 = 4050

n^3 = 4050 / 0.0012
n^3 = 3,375,000
n = ³√3,375,000
n = 150

That's all you have to do, hope this helped. :)
 
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