F.3 mathz1問(percentage change)! 吾該幫幫忙!

2008-10-07 7:32 pm

plz help me to answer the following questions;;i need the steeps;;thz for your help=)

1)If the radius of a circle is increased by 10%,find the percentage increase in its area.

2)If the height of a triangle is increased by 30% while its base is dreased by 25%,what is the percentage change in its area?

3)There are 800 students in a school,37.5% of them are girls.If the number of boys and girls are increased by 20% and 10% respectively,What is the percentage change in the number of students?

回答 (1)

Jonathan

2008-10-07 8:02 pm

✔ 最佳答案

Q.1
Area of circle is 3.14 x (R^2), if R is increased by 10%, then the new area should be:-
= 3.14 x (R+10%)^2
= 3.14 x (1.1R)^2
= 3.14 x 1.21 x R^2

So, the area is increased by 21%

Q.2
Area of triangle is (h x b) / 2, if h is increased by 30% and base is decreased by 25%, the new area should be:-
= (h+30%) x (b-25%) / 2
= (1.3h x 0.75b) / 2
= ( 0.975 h x b ) / 2

So, the area is decreased by 2.5%

Q.3
Original number of girl = 800 x 37.5% = 300
Original number of boy = 500
New number of girl = 300 x (1+10%) = 330
New number of boy = 500 x (1+20%) = 600
So, new number of total students = 930

% change = (930-800) / 800 x 100%
= 16.25%c (increased)

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