數學題目(應用題)

設女為x, 男為2x
x + 2x + 6 = 120
3x + 6 = 120
3(x + 2) = 120
x + 2 = 40
x = 38
therefore 男有38x2 = 76人
1.
x + 2y = 9
y = 2x - 3

x + 2(x - 3) = 9
x + 2x - 6 = 9
3x = 15
x = 5

5 + 2y = 9
2y = 4
y = 2

therefore x = 5, y = 2
2. 3x + y = 11
-3 + 2y = 10

-3 + 2y = 10
2y = 13
y = 6.5
3x + 6.5 = 11
3x = 4.5
x = 1.5
therefore x = 1.5, y = 6.5

1. 設小的為x, 大的為y
x + y = 37
y - x = 13

y = 13 + x

x + 13 + x = 37
2x = 24
x = 12
12 + y = 37
y = 25
therefore the two no. are 12 and 25
設秋美為x, 女兒為y
x - y = 30
(x + 3) = (y + 3)3
x + 3 = 3y + 9
x = 3y + 6

3y + 6 - y = 30
2y = 24
y = 12

x - 12 = 30
x = 42
there fore 秋美是42歲, 女兒是12歲

1.
假設男觀眾有x位; 女觀眾有y位.
x = 2y
y+6 + x = 120

y+6 + 2y = 120
3y + 6 = 120
y = 38
x = 2y = 76

∴有76位男觀眾.

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1.
x+2y = 9
y=2x-3

x + 2(2x-3) = 9
x + 4x - 6 = 9
x = 3
y = 2x - 3 = 3

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2.
3x + y = 11
-3 + 2y = 10

y = 11 - 3x
-3 + 2(11 - 3x) = 10
-3 + 22 - 6x = 10
-10 - 3 + 22 = 6x
x = 3/2 = 1.5
y = 11 - 3x = 6.5

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1.
假設兩數分別係x 及y, 而x為較大者.

x + y = 37
x - y = 13

(兩式相加)
2x = 50
x = 25
y = 37 - 25 = 12

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2.
假設秋美是x歲, 她女兒是y歲.

x - y = 30
x + 3 = 3(y + 3)

x = 30 + y
30 + y + 3 = 3(y + 3)
33 + y = 3y +9
24 = 2y
y = 12
x = 30 + y = 42

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希望幫到你啦~~^^

男觀眾的人數=2x
女觀眾的人數=x
2x+x+6=120
3x=114
x=38
女觀眾的人數=38
男觀眾的人數=2(38)=76


1.
x+2y=9-----*
y=2x-3------**
put ** into *, we have
x+2(2x-3)=9
5x=15
x=3
put x=3 into *, we have
2y=9-3
y=3
thus, x=3, y=3


2.3x+y=11
-3+2y=10
係咪漏左個x, -3x+2y=10??
x=4/3
y=7

解決以下問題
1.若兩數之和為37,差為13,求該兩個數。
設最細既為x, 則另一個係x+13
x+x+13=37
2x=24
x=12
該兩個數是12和25
2.秋美與女兒的年齡相差30歲。3年後,她的年齢是女兒的三倍,
求秋美與她女兒現在的年齢。
秋美現在的年齡=x+30
女兒現在的年齡=x
3(x+3)=x+30+3
3x+9=x+33
2x=24
x=12
秋美現在的年齡=42
女兒現在的年齡=12

1--76
2--X=3 Y=3
3--X=1.5 Y=6.5
4--X=25 Y=12
5--X=15 Y=45