math pls answer it~ thanks

Q1.

The surface of the cone is coloured. It is cut 3 times as shown below. How many 3-D shapes cut out have two sections that are not coloured?


Ans:

After 3 cuts, there are total 6 pieces 3-D shape formed.

From the figure, you can count out from the cone that the top 2 pieces and the bottom 2 pieces have 2 sections not coloured.

Therefore, there are total 4 pieces 3-D shape that are not coloured.




Q2

Look at the figure on the left. What percentage of the length of "Big Circle" is the length of "String"?


Ans:

(i)

the radius for the big circle = 7cm,

therefore, the circumference of big circle = 2 x r x pi = 2 x 7 x 3.14 = 43.96 cm


(ii)

the radius of the string = 1/2 x 7cm = 3.5cm

the lenght of the string = circumference of small circle = 2 x 3.5 x 3.14 = 21.98 cm


so, the percentage of circumference of big circle to the string is 43.96/21.98 x 100% = 200%

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