maths questions:

there are 130 coins in a box, which includes $1-coins and 50仙-coins only.
(a)let x be the number of$1-coins.Use an algebraic expression to repesent the total value of the coins
65+x/2 (這式不正確)
因為有 x 個 $1 硬幣，所以有 130 – x 個 50仙的硬幣
正確的式應為
x + (130 – x)/2


(b)Given that the value of the coins i s $107.
(i)Set up an algebraic equation in x and solve it.
x + (130 – x)/2 = 107 (全式乘2)
2x + 130 – x = 214
x = 214 – 130
x = 84
及有 130 – x = 46個50仙硬幣

(ii)Find the difference between the numbers of the two kinds of coins.
兩者相差
84 – 46 = 38
一元的比50仙多38個

a)
x + (130-x) *0.5

b)
i)
x + (130-x) * 0.5 = 107
x + 65 -0.5x = 107
0.5 x = 107 - 65
x = 42 * 2
x = 84

ii)
number of $1 = 84
number of 50 cent = 130 - 84 =46

difference = 84 - 46 = 18
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Your question
Why(b)(i)the answer is 65+x/2=107
65+x/2=107 is the same as x + (130-x) * 0.5 = 107

x + (130 - x) * 0.5 = 107 is easier to understand.

2006-11-17 12:39:37 補充：
Sorry for mistakedifference = 84 - 46 = 38