幫幫忙!!勁急!!!(數學題) (10分)

1 a/2 + 5.5 = 9.8 - 3a/5
(2+a)/2 + 3a/5 = 4.3
(2+a)*5 + 3a*2 = 43 (全條式乘 10)
10+5a + 6a = 43
11a = 33
a = 3


3a/4 - 0.25a + 2.8 = 5a/24 + 3.5
3a*6 - 6a + 67.2 = 5a + 84 (全條式乘 24)
18a - 6a - 5a = 16.8
7a = 16.8
a = 2.4


3.25a + 3 1/5 = 2(1 a/4 + 2) + 1 1/8
3.25a + 16/5 = 2(4+a/4 + 2) + 9/8
130a + 16*8 = (4+a)*20 + 4*40 + 9*5 (全條式乘 40)
130a + 128 = 80 + 20a + 160 + 45
110a = 157
a = 157/110


設弟分得a粒, 哥分得b粒
a+b = 52 -- (i)
b*(1 1/6) = a
b*7/6 = a -- (ii)
sub (ii) into (i),
7b/6 + b = 52
7b + 6b = 312
13b = 312
b = 24
a = 52-24
a = 28
弟分得 24 粒, 哥分得 28 粒


設西瓜原有a公斤
a/3 = 3 (因為吃掉的 3 公斤剛好是西瓜的 1/3)
a = 9
西瓜原有 9 公斤


設哥哥是a歲
2a/3 = a - 5
2a = 3a - 15
a = 15
哥哥今年 15 歲, 弟弟則是 10 歲


設乙車每小時行a公里
210 - 3*45.5 = 3a
210- 136.5 = 3a
a = 73.5 / 3
a = 24.5
乙車每小時行 24.5 公里


設長方形的闊度是a cm
[a+ (a+21)]*2 = 646
4a + 42 = 646
4a = 604
a = 151
長方形的闊度是 151 cm

1又2分之1a + 5.5 = 9.8 - 5分之3a
(3 / 2) a + 11 / 2 = 49 / 5 - (3 / 5) a
(3 / 2) a + (3 / 5) a = 49 / 5 - 11 / 2
(15 / 10) a + (6 / 10) a = 98 / 10 - 55 / 10
(21 / 10) a = 43 / 10
a = 43 / 21
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4分之3a - 0.25a + 2.8 = 24分之5a + 3.5
(3 / 4) a - (1 / 4) a = (5 / 24) a + 3.5 - 2.8
(2 / 4) a - (5 / 24) a = 0.7
(12 / 24) a - (5 / 24) a = 7 / 10
(7 / 24) a = 7 / 10
a = 24 / 10
a = 2.4
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3.25a + 3又5分之1 = (1又4分之1a + 2) x 2 + 1又8分之1
(13 / 4) a + 16 / 5 = (9 / 4) a + 4 + 9 / 8
(13 / 4) a - (9 / 4) a = 4 + 9 / 8 - 16 / 5
(4 / 4) a = 4 + 1.125 - 3.2
a = 1.925
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兄弟二人分糖果52粒,哥哥分得的是弟弟分得的1又6分之1.
1) a + b = 52
2) a = (7 / 6) b

(7 / 6) b + b = 52
(7 / 6) b + (6 / 6) b = 52
(13 / 6) b = 52
b = 24

a + 24 = 52
a = 28
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一個西瓜,吃掉了3公斤,剛好是3分之1,這西瓜原來有多重?
(設西瓜原有a公斤)
(1 / 3) a = 3
a = 9
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哥哥比弟弟大5歲,弟弟今年剛好是哥哥年歲的3分之2,哥哥是幾歲?
(設哥哥是a歲, 弟弟是b歲)
1) a = 5 + b
2) a = (3 / 2) b

(3 / 2) b = 5 + b
1.5b - b = 5
0.5b = 5
b = 10

a = 5 + b
a = 5 + 10
a = 15
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兩地相距210公里,甲乙兩車從兩地相對開出3小時後相遇. 已知甲車每小時行45.5公里,乙車每小時行多少公里?
(設乙車每小時行a公里)
例式+答案
a=?

210 km = (45.5 km/hr + a) * 3 hr
70 km/hr = 45.5 km/hr + a
a = 24.5 km/hr
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一個長方形的長度比闊度長0.21m,周界是646cm,該長方形的闊度是多少cm?
(設長方形的闊度是a cm, 長度是b cm)
1) a + 21 cm = b
2) 2a + 2b = 646 cm

a + b = 323 cm
a + (a + 21) = 323 cm
2a = 302 cm
a = 151 cm