Pure Maths

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Two cones are similar in shape and the ratio of corresponding lengths is 3:5.

(a) if the radius of the smaller cone is 12cm, find the radius of the larger cone.
(b) if there is sufficient paint to paint 216 large cones, how many smaller cones can be painted with same amount of paint?
(c) If the same amount of paint covers 24 similar cones, what is the radius of one of these cones?

Question (a) is straight forward but I would really appreciate help with questions (b) and (c). My head is starting to hurt :-)

• Pure Maths -

linear dimensions scale in the ratio of 3:5

areas scale in the ratio of (3:5)^2 = 9:25

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