8條f.1數學應用題.急!20 points

Question 18.

(n + 2)
------------------- x100 = 60
(2n + 2 - 40)

(n + 2)
--------------- = 0.6
(2n - 42)

n + 2 = 0.6(2n - 42)
n + 2 = 1.2n – 25.2
2 + 25.2 = 1.2n – n
27.2 = 0.2n
n = 27.2/0.2
n =136

Question 19.
(10% + 20% + 40%) = 70%
She spent 70% of her saving on buying things
She still had 30% of her saving left which is $600
Original amount of her saving = ($600/30) x 100
Original amount of her saving = $2000

Question 20. Typo error. Check all the numbers.

Question 21. Typo error. Please check the wording.
Amy is 80% of Cindy’s height. Cindy is taller than Amy.

Question 22.
Area of a triangle = ½ (base x height)
Height = 2 x area/base = 2 x 22.5c㎡/ 9cm = 5 cm
Original base = 9 cm/0.9 = 10 cm

(a) original area of the triangle = ½ (base x height) = ½ (10 cm x 5 cm)
Original area of the triangle =25 c㎡

(b) percentage change in the area = (change in area/original area)x 100%
percentage change in the area
= (22.5 – 25) /25 x 100% = -2.5/25 x 100% = -10%
Percentage change in the area = 10% (decreasing)

Question 23.
(a) The cost of doll = [$178/(100 -20) ]x 100 = [$178/80]x100
The cost of doll = $222.50

(b) Selling price =$222.50 + $222.50 x 20/100 = $222.50 + $44.50 = $267
Selling price should be $267

Question 24.
Cost of suitcase = $600/(100 – 20) x 100 = $750
If the suitcase sell at $690, it is still a loss.
Loss percentage = [(690 – 750)/750] x 100 = -8%
Negative sign indicates it is a loss.
8% loss if sold at $690

2011-02-10 10:23:50 補充：
Ques 18: (correction)
(n + 2)
------------------- x100 = 60
(2n + 2 - 40)

(n + 2)
--------------- = 0.6
(2n - 38)

n + 2 = 0.6(2n - 38)
n + 2 = 1.2n – 22.8
24.8 = 0.2n
n = 24.8/0.2
n =124

2011-02-10 10:43:38 補充：
Ques 21:

Bonnie’s height = h
Amy’s height = 0.8 h
Bonnie’s height/Cindy’s height = h/Cindy’s height = 80/100
Cindy’s height = h/0.8 = 1.25h
Amy’s height /Cindy’s height x 100% = (0.8h)/(1.25h) x 100% = 64%
Amy's height is 64% of Cindy’s height

2011-02-10 11:02:28 補充：
Ques 20:
x/(190 + 230) = 10/100
x = 42

If x cans pork and x cans fish
2x/(190 + 230) = 10/100
x = 21

2011-02-10 11:47:53 補充：
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