math question F.1

2007-12-07 4:04 am

1.The side of a cube is 15 cm long.if each side of the cube increases by 20% , find the percentage increase in its volume.

2. if each side of a cube decreases by 10% , find the percentage decrease in its volume.
[ Hint: let each side of the original cube be L cm long.]
第二題不是承上題,點解&點做

回答 (1)

harry sze

2007-12-07 4:18 am

✔ 最佳答案

1. cube 即係立方體...volume=side x side x side=side^3
the new cube side :15x(1+20%)=15x1.2=18cm
the new cube volume:18x18x18=5832cm^3
the old cube volume:15x15x15=3375cm^3
the percentage increase in its volume:
(5832-3375)3375x100%=72.8%
increase72.8%
2.let each side of the original cube be L cm long
the new side :Lx(1-10%)=Lx0.9=0.9Lcm
the new volume:0.9Lx0.9Lx0.9L=0.729L^3cm^3
the old volume:LxLxL=L^3cm^3
the percentage decrease in its volume:
(0.729L^3-L^3)/L^3x100%
=-0.271/1x100%=-27.1%
decrease27.1%

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