F.1 數學問題 急 20點!

the percentage
=1-0.56
=0.44

the percentage
=15*15/15*(1+0.2)*15*(1+0.2)*100%
=225/324*100%
=25/36

2012-11-17 15:07:49 補充：
Correction
the percentage
=15*15/15*(1+0.2)*15*(1+0.2)*100%
=225/324*100%
=25/36

change to
the percentage
=15*15/15*(1+0.2)/15*(1+0.2)*100%
=225/324*100%
=25/36

2012-11-20 16:32:28 補充：
Correctoins ;
the new side
=15*(1+20%)
=18cm
the new area
=18*18
=324cm2
the % increase
=(324-15*15)/15*15*100%
=(324-225)/225*100%
=99/225*100%
=44%

1) x and y are positive numbers.
x=0.56y
the percentage of x less than y :
(y-x)/y。100%
=(y-0.56y)/y。100%
=0.44y/y。100%
=0.44。100%
=44%

2) for "any square", if each side increased 20%, the percentage increase in area is:
(1 + 20%)^2 - 100%
=120%^2 - 100%
=144%-100%
=44%

2012-11-18 04:08:04 補充：
The question 2 is only asking for the percentage and is no matter about the length of sides.

2012-11-20 09:36:41 補充：
2)A square of side 15 cm , if each side is increased by 20% find the percentage increase in area.

I have to point out that the percentage increase is base on the original size, not the new one.
the original square's area is 15^2=225
the new square's area is (15x120%)^2=(15x1.2)^2=18^2=324

2012-11-20 09:41:26 補充：
so the percentage increase in area is
(324-225)/225。100%
=99/225。100%
=44%
The concept is very importance. Please don't be confused while studying.

2012-11-20 09:42:35 補充：
*for all buddies*

1)
the precentage
=[(y-x)/y]*100%
=[(y-0.56y/y)]*100%
=[0.44]*100%
=44%

2)
the original size
=15*15
=252cm^2

the new size
=[15(1+20%)]^2
=[15(1.2)]^2
=324cm^2

the percentage increase
=(324-252)/252*100%
=72/252*100%
=28.6%(corr to 3 sig fig)

Answer: 44%

Solution:

the percentage
= [(y - x) / y] x 100%
= [(y - 0.56y) / y] x 100%
= (0.44y / y) x 100%
= 0.44 x 100%
= 44%

2012-11-22 15:49:12 補充：
Answer for Q2: 44%

Solution:

original area = 15 x 15 = 225 cm^2
new area = [15 x (1 + 20%)] x [15 x (1 + 20%)] = 324 cm^2

the percentage increase in area
= [(324 - 225) / 225] x 100%
= (99 / 225) x 100%
= 44%