F.1 方程2條((-10分

1. (7) A student bought a pen at $5 and some writing pads at $15 each . If the total cost of the pen and the writing pads was $65, how many writing pads did he buy ?

Let the number of the writing pads he bought be x，
5 + 15x = 65
5 + 15x – 5 = 65 – 5
15x ÷ 15 = 60 ÷ 15
x = 4
∴He bought 4 sets of writing pads.


2. (11) Helen goes to work by MTR and bus . She spends 35 minutes more on the MTR than on the bus . The whole journey takes her 55 minutes . How long does she spend on the bus ?

Let she spends x minutes on the bus,
35 + x = 55
35 + x – 35 = 55– 35
x = 20
∴She spends 20minutes on the bus.

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2008-10-13 22:00:49 補充：
對不起, 第二題要修正:

Let she spends x minutes on the bus,
35 + 2x = 55
35 + 2x – 35 = 55– 35
2x ÷ 2 = 20 ÷ 2
x = 10
∴She spends 10minutes on the bus

2008-10-14 11:24:05 補充：
• 現回應你在 [ 2008-10-13 22:36:40 補充 ] 的問題：
3. (15) If the sum of two consecutive odd numbers is 20, find the smaller number .
Let x be the smaller number.
x + x + 2 = 20
2x + 2 - 2 = 20 – 2
2x ÷ 2 = 19 ÷ 2
x = 9
∴The two consecutive odd numbers are 9 and 10 respectively.

2008-10-14 11:24:19 補充：
4. (19) In a class of 45 students , the number of girls is more than the number of boys by 11 .

(a) How many girls are there in the class ?
Let the number of girls in the class be x.
x + x – 11 = 45
2x – 11 + 11 = 45 + 11
2x ÷ 2 = 56 ÷ 2
x = 28
∴The number of girls in the class is 28.

1. 5+15x=65
x=4
he bought 4writing pads
2. x+x+35=55
2x=20
x=10
she spends 10mins on the bus

慢慢解就做到啦~ 唔洗擔心~~

第一條 :

一個學生買左一支筆同唔知幾多個Writing pads~~ 一支筆係 5 蚊, 一個 writing pad 係 15 蚊, 共俾咗 65 蚊.

答案如此 : 假設佢買咗 Y 個 writing pads,

$15 x Y + $5 = $65

15Y = 65 - 5

15Y = 60

so, Y = 4

即係共買了 4 個 Writing pads.

第二題 :

海倫佢番工, 坐地鐵比坐巴士耐 15 分鐘. 如果地鐵要 55 分鐘, 咁坐巴士要幾耐?

假說坐巴士的時間為 Z,

Z + 15 = 55

Z = 55 - 15

Z = 40

所以坐巴士只要 40 分鐘!