math~急

1. 4+3w/8=-2
　　3w/8 = -6
　　　3w = -48
　　　 w = -16

2. y+9-7y/11=0
　y+9 = 7y/11
　11y+99 = 7y
　　　4y = -99
　　　 y = -99/4　= 24 3/4

3. p+3/5=3p/10-p/2
　10p + 6 = 3p - 5p　[全式乘 10]
　　12p = -6
　　　p = -1/2

4.8(x+3)=-5(6-2X)
　8x + 24 = -30 + 10x
　　　2x = 54
　　　 x = 27

5. 2(5x-1)-(7x+3)=10　[原本題目少左一個關括號，希望冇擺錯位]
　10x - 2 - 7x -3 = 10
　　3x -5 = 10
　　　3x = 5
　　　 x = 5/3　= 1 2/3

6. -3(a+1)+2(9-2a)+6=0
　-3a - 3 + 18 - 4a + 6 = 0
　　　7a = 21
　　　 a = 3

7. 9-y=7(3+y)-4(3y+1)
　9-y = 21 + 7y - 12y -4
　9-y = 17 -5y
　 4y = 8
　　y = 2

8.12(2y-3)=-8-4(7-3y )
　24y-36 = -8 -28 +12y
　　12y = 0
　　　y = 0

9.5y-[7+2(3y-8)]=10+ y
　5y-[7+6y-16] = 10+y
　5y-6y+9 = 10+y
　　　　2y = -1
　　　　 y = -1/2

10. 9+2[a-(4-3a)]=6a-13
　　9+2[a-4+3a]=6a-13
　　9+8a-8 = 6a-13
　　　　2a = -14
　　　　 a = -7

11. if a number is subtracted from 12 and the difference is then multiplied by3.
　the product is42. find the number .

　Let x be the number:
　　(x-12)*3 = 42
　　　x-12 = 14
　　　　x = 26
　The number is 26.

12. there are some $2 coins and some$5coins.
　the total value is $169 and the total nimber of coinsis 50.
　find the number of $2coins.

　Let m be the number of $2 coins
　and n be the number of $5 coins

　Given that,　m+n = 50
　　　　　　　n = 50-m　--- [1]
　and　2m + 5n = 169　--- [2]
　
　Put [1] into [2]
　　　　2m + 5(50-m) = 169
　　　　2m + 250-5m = 169
　　　　　　　　3m = 81
　　　　　　　　　m = 27

　The number of $2 coins is 27.

1. 4+3w/8=-2
　　3w/8 = -6
　　　3w = -48
　　　 w = -16

2. y+9-7y/11=0
　y+9 = 7y/11
　11y+99 = 7y
　　　4y = -99
　　　 y = -99/4　= 24 3/4

3. p+3/5=3p/10-p/2
　10p + 6 = 3p - 5p　[全式乘 10]
　　12p = -6
　　　p = -1/2

4.8(x+3)=-5(6-2X)
　8x + 24 = -30 + 10x
　　　2x = 54
　　　 x = 27

5. 2(5x-1)-(7x+3)=10　[原本題目少左一個關括號，希望冇擺錯位]
　10x - 2 - 7x -3 = 10
　　3x -5 = 10
　　　3x = 5
　　　 x = 5/3　= 1 2/3

6. -3(a+1)+2(9-2a)+6=0
　-3a - 3 + 18 - 4a + 6 = 0
　　　7a = 21
　　　 a = 3

7. 9-y=7(3+y)-4(3y+1)
　9-y = 21 + 7y - 12y -4
　9-y = 17 -5y
　 4y = 8
　　y = 2

8.12(2y-3)=-8-4(7-3y )
　24y-36 = -8 -28 +12y
　　12y = 0
　　　y = 0

9.5y-[7+2(3y-8)]=10+ y
　5y-[7+6y-16] = 10+y
　5y-6y+9 = 10+y
　　　　2y = -1
　　　　 y = -1/2

10. 9+2[a-(4-3a)]=6a-13
　　9+2[a-4+3a]=6a-13
　　9+8a-8 = 6a-13
　　　　2a = -14
　　　　 a = -7

11. if a number is subtracted from 12 and the difference is then multiplied by3.
　the product is42. find the number .

　Let x be the number:
　　(x-12)*3 = 42
　　　x-12 = 14
　　　　x = 26
　The number is 26.

12. there are some $2 coins and some$5coins.
　the total value is $169 and the total nimber of coinsis 50.
　find the number of $2coins.

　Let m be the number of $2 coins
　and n be the number of $5 coins

　Given that,　m+n = 50
　　　　　　　n = 50-m　--- [1]
　and　2m + 5n = 169　--- [2]
　
　Put [1] into [2]
　　　　2m + 5(50-m) = 169
　　　　2m + 250-5m = 169
　　　　　　　　3m = 81
　　　　　　　　　m = 27

　The number of $2 coins is 27.

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