兩條F1數學..附請步驟{{急!!}}

1.) 設有$2硬幣x個, 那麼$5硬幣有12-x個
2x + 5(12-x) = 39
2x+60-5x = 39
3x = 21
x = 7
所以有$2硬幣7個, $5硬幣有5個.

2.)設有x粒橙味, 那麼有18-x粒芒果味
5x + 8(18-x) = 111
5x+144-8x = 111
3x = 33
x = 11
所以有11粒橙味, 有7粒芒果味.

1)
小強有$2硬幣和美5硬幣共12個，總值為＄39。問$2硬幣和$5硬幣分別有幾多個?

設有$2硬幣y個, 那麼$5硬幣有(12-y)個
2y + 5(12 - y) = 39
2y + 60- 5y = 39
3y = 21
y = 7
所以有$2硬幣7個, $5硬幣有5個

2)
小明購買18粒糖$111,橙味$5,芒果$8.求每種糖的數量

設有a粒橙味, 那麼有(18-a)粒芒果味
5x + 8 (18 - a) = 111
5x +144 - 8a = 111
3a = 33
a = 11
所以有11粒橙味, 有7粒芒果味

小強有$2硬幣和5硬幣共12個，總值為＄39。問$2硬幣和$5硬幣分別有幾多個

設小強有$2硬幣x,$5硬幣y
x+y=12................1
2x+5y=39.............2

sub 1 into 2
2x+5(12-x)=39
2x+60-5x=39
21=3x
x=7

7+y=12
y=5


小明購買18粒糖$111,橙味$5,芒果$8.求每種糖的數量
橙味:x,芒果:y

5x+8y=111.........1
x+y=18.........2

sub 1 into 2
5x+8(18-x)=111
33=3x
x=11

11+y=18
y=7

設$2硬幣為ｘ，
２（ｘ）＋５（１２－ｘ）＝３９
　　　　２ｘ＋６０－５ｘ＝３９
　　　　　　　　　－３ｘ＝－２１
　　　　　　　　　　　ｘ＝７

設橙味有ｘ粒糖，
５（ｘ）＋８（１８－ｘ）＝１１１
　　　５ｘ＋１４４－８ｘ＝１１１　
　　　　　　　　　－３ｘ＝－３３
　　　　　　　　　　　ｘ＝１１　

let x be the no. of $2 and y be the no. of $5.
2x + 5y =39; x + y =12
i.e. x = 12 - y

2(12 - y) + 5y = 39
24 - 2y + 5y = 39
3y = 15
y = 5

then put y=5 into the x + y =12
x + 5 = 12
x = 7

i.e the no. of $2 is 7 and the no. of $5 is 5



Let x be the no. of orange and y be the no. of mango
5x + 8y = 111
x + y = 18
i.e. x = 18 - y

5(18 - y) + 8y = 111
90 - 5y + 8y = 111
3y = 21
y = 7

put y = 7 into x + y = 18
x + 7 = 18
x = 11

so the no. of orange is 11 and the no. of mango is 7

小強有$2硬幣和5硬幣共12個，總值為＄39。問$2硬幣和$5硬幣分別有幾多個

設小強有$2硬幣x,$5硬幣y
x+y=12................1
2x+5y=39.............2


2x+5(12-x)=39
2x+60-5x=39
21=3x
x=7

7+y=12
y=5


小明購買18粒糖$111,橙味$5,芒果$8.求每種糖的數量
橙味:x,芒果:y

5x+8y=111.........1
x+y=18.........2

5x+8(18-x)=111
33=3x
x=11

11+y=18
y=7

小強有$2硬幣和5硬幣共12個，總值為＄39。問$2硬幣和$5硬幣分別有幾多個

設小強有$2硬幣x,$5硬幣y
x+y=12................1
2x+5y=39.............2

sub 1 into 2
2x+5(12-x)=39
2x+60-5x=39
21=3x
x=7

7+y=12
y=5


小明購買18粒糖$111,橙味$5,芒果$8.求每種糖的數量
橙味:x,芒果:y

5x+8y=111.........1
x+y=18.........2

sub 1 into 2
5x+8(18-x)=111
33=3x
x=11

11+y=18
y=7

設$2係x $5係y lo

2x + 5y= 39 (1)
x+y =12
x = 12-y (2 )
sub 2 into (1)

2(12-y) + 5y =39
y=???﹒自己計^^

第2題: x +y = 18
x= 18-y (1)
5x + 8y = 111(2)
sub 1 into 2
5(18-y) + 8y =111
y=???/
自己計^^