# Mathswatch

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#1
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#2
Question 3b page 3 (118C
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3 years ago
#3
(Original post by Official-21)
Question 3b page 3 (118C
Diameter = 12cm

Lowest multiple of 12 under 50 is 48
48 /12 = 4

Lowest multiple of 12 under 100 is 96
96 / 12 = 18

4 CDs can be cut across the height, 8 CDs can be cut across the width.

Hence 8 x 4 = 32 CDs can be cut. This is assuming you are allowed to waste extra plastic or stick 2 pieces together in some way.

Diagram on next comment.
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3 years ago
#4
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#5
Why cant you just do area of rectangle devided by area of circle
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3 years ago
#6
(Original post by Official-21)
Why cant you just do area of rectangle devided by area of circle
Because once you cut out the 32 CDs, the remaining plastic will not be round. In order cut out more CDs, you would need to stick pieces of plastic together which the question doesn't say you can do.
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#7
where did you get 32 cd's from
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3 years ago
#8
(Original post by Official-21)
where did you get 32 cd's from
The diameter of the circle is 12cm. This means the smallest bit of square plastic you can cut a CD from is 12cm x 12cm.

4 CDs can fit the height (50cm) of the plastic with 2 cm left over.
8 CDs can fit the width (100cm) of the plastic with 4 cm left over.
4 (in height) x 8 (in width) = 32 CDs.

The remainder of the card would not be big enough to cut out CDs from. You cannot cut more circles as you cannot stick 2 pieces of plastic together to make a CD.

Area circle = (6^2) x pi = 36pi
Area of plastic sheet = 50cm x 100cm = 5000 cm^2
5000 / 36pi = 44.21 (2dp)
32 CDs could be cut, but 44 CDs could be cut if you could stick plastic together to make a CD.
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