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This question gave me headache. Hope answers are correct 🙂

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The answer is correct. Thanks for your help

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(a) Total painted area = 2(  5 * 4 + 10 * 5 + 10 * 4) = 220 cm²

(b) (i) none of the faces painted are those cubes that are not at the surface of the block

= 3 * 2 * 8 = 48  

Note : the length of the inner block are all  of each dimension – 2 cm. For example, breadth = 10 -2 = 8 etc.

(ii) cubes that have 2 surfaces painted are cubes that are at the edge of the block excluding those that are at the corners.

The number of cubes with 2 surfaces painted are = 8 * 4 + 2 * 4 + 3 * 4 = 32 + 8 + 12 = 52

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Just a note on wording of question: 2 of the faces painted; does that include those with 3 faces painted (logically, yes).

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I am not sure on this. But imho, there should be difference between 2 of the faces painted with 3 faces painted. It should be phrased as “at least 2 of the faces painted” if want to include 3 faces painted’s cubes. Perhaps VIP can update us on the answer given by the teacher.

 

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