f.1 maths

2006-11-15 4:49 am

1. Mary is now three times as old as Susan. Three years ago, the sum of their ages was 22. How old is Susan now?

2. In 8 years' time, Tom will be twice as old as he was 8 years ago. How old is he now?

3. One number is 7 times that of another number. Their difference is 54. What are the numbers?

更新1:

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回答 (4)

Pak Hong

2006-11-15 5:04 am

✔ 最佳答案

1.Let a be Mary's year old now.

a + 3a=22+6
a+3a=28
4a=28
a=7

Susan's year old now : 7 x 3 = 21

2. Let a be Tom's year old now.

2a=a+8
a=8

Tom's year old now : 8+8=16

3. Let th smaller number be a .

7a - a = 54
6a=54
a=9

the larger number : 7 x 9 = 63

the numbers are 63 and 9

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chantsz

2006-11-15 5:05 am

1. Let the age of Susan be X
(3X-3)+(X-3)=22
3X-3+X-3=22
4X=28
X=7
SO Susan is now 7 years old.

2.Let the age of Tom be X
X+8=2X
X=8
SO Tom is now 8 years old.

3.Let the smaller number be X
7X-X=54
6x=54
X=9
SO the smaller number is 9.
the bigger number is 63.

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jen

2006-11-15 4:59 am

1.Let the age of Susan be y years old.
(y-3)+(3y-3)=22
y-3+3y-3=22
4y-6=22
y=7
∴Susan is 7years old now//
2.Let Tom is X years old now.
X+8=2X
8=2X-X
X=8
∴Tom is 8 years old now//
3.Let the number be Z.
7Z-Z=54
6Z=54
Z=9
∴The number is 9//
希望冇計錯喇^v^"

2006-11-14 21:03:56 補充：
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lawrence

2006-11-15 4:54 am

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