Word problem

不好意思.妳還記得我答過妳這條問題嗎?? 謝謝妳選了我為最佳答案, 以下那一題, 我答錯了. 不好意思喔~~~~~
12. x/4-x+1/8=2
(x/4-x+1/8) * 8 = 2 * 8
2x - 8x + 8 = 16
-6x = 16 - 8
-6x = 8
x = - 4/3
正確應是 :
12. x/4-x+1/8=2
(x/4-x+1/8) * 8 = 2 * 8
2x - 8x + 1 = 16
-6x = 16 - 1
-6x = 15
x = - 2.5

2006-10-19 20:45:36 補充：
20. LET X AND Y BE THE 2 DOLLARS STAMPS AND 5 DOLLARS STAMPS WHICH DONNA BYS RESPECTIVELY.X + Y = 15---------(A)2X + 5Y = 54------------(B)FROM (A), X + Y = 15 X = 15 - Y ----------- (C)

2006-10-19 20:45:55 補充：
INSERT (C) INTO (B),2X + 5Y = 542* (15-Y) + 5Y = 5430 - 2Y + 5Y = 543Y = 54 - 303Y = 24Y = 8FROM (C), X = 15 - Y X = 15 - 8 X = 7.THEREFORE, DONNA BUYS 7 - 2 DOLLARS STAMPS.

2006-10-19 20:50:08 補充：
19) LET X AND Y BE THE NUMBERS OF GIRLS AND BOYS RESPECTIVELY.X + Y = 45 --- (A)Y = X - 11------(B)INSERT (B) INTO (A),X + Y = 45X + (X - 11) = 452X - 11 = 452X = 45 + 112X = 56X = 28THEREFORE, THERE ARE 28 GIRLS IN THE CLASS.

2006-10-19 20:51:59 補充：
FROM (B), Y = X - 11 AND WE KNOW X = 28, Y = 28 - 11 Y = 17THEREFORE, THERE ARE 11 BOYS IN THE CLASS.

2006-10-19 21:05:27 補充：
16.) 3/4x-2(x-24)=3 3/4x - 2x + 48 = 3 3/4x - 2x = 3 - 48 3/4x - 2x = -45 -1.25x = - 45 x = 36

20. Donna buys some 2 dolars stamps and some 5 dollars stamp,if she spends 54 dollars altogether and gets 15 stamps,how many 2 dollars does she buy?
let x be the number of $2 stamp,then the number of $5 stamp is 15-x
2x+5(15-x)=54
2x+75-5x=54
75-3x=54
3x=21
x=7
so she buys 7 $2 stamps

19.In a class of 45 students, the number of girls is more than the number of boy by11.
(1)how many girls are there in the class?
let x be the number of girls in the class
then the number of boys is x-11
x+(x-11)=45
2x-11=45
2x=56
x=28
so there are 28 girls in the class.

(2)how many boys are there in the class?
the number of boys =45-28 =17
so there are 17 boys in the class.


16. 3/4x-2(x-24)=3
3/4x-2x+48=3
45=5/4 x
x=36

20.7 2dolars stamps

19.(1)34
(2)11
16. Do not know

let she buys x 2 dollars stamps ,y 5 dollars stamp
then
x+y=15
2x+5y=54
from (1)
y=15-x
2x+5(15-x)=54
-3x=-21
x=7
she buy 7 "2 dolars stamps "
19
let there are x boys
then there are x+11 girls
x+x+11=45
x=17
so there are 17 boys ,28 girls
3/4x-2(x-24)=3
3x-8x+192=12
-5x=-180
x=36

20. ans is 7
19. 28girls

17boys