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神秘人

2008-07-21 7:54 pm

1. think of a number, multiply it by 3 and add 7 ; the result is 43 .what is the number?

2. think of a number , double it and add 4; the result is 30. find the number.

3. one number is three times another and their sum is 36. find the numbers .

4. the sum of two numbers is 63 and one of them exceeds the other by 7 . find the numbers

5. the sum of two numbers is 27 and one of them exceeds twice the other by 3.what are the numbers?

回答 (1)

Maggie & Jo

2008-07-21 8:25 pm

✔ 最佳答案

1. 找一個數字, 這數字乘3之後再加7, 會等於43.
-----> 將數字假設為X:
3X + 7 = 43
3X = 43 - 7
3X = 36
X = 12

2. 找一個數字, 這數字乘2之後再加4, 會等於30.
-----> 將數字假設為X:
2X + 4 = 30
2X = 30 - 4
2X = 26
X = 13

3. 有一個數字是另一個數字的3倍, 如果這兩個數字相加等於36, 請找出這兩個數字.
------>假設這兩個數字分別是 X , Y:
1. Y = 3X

2. X + Y = 36
X + (3X) = 36
4X = 36
X = 9

9 + Y = 36
Y = 25

4. 有兩個數字, 它們的和是63, 大的比小的大7, 請找出這兩個數.
----->假設這兩個數字分別是 X , Y:
1. X + Y = 63
2. Y = X + 7X

X + ( X + 7 ) = 63
2X + 7 = 63
2X = 56
X =28

28 + Y = 63
Y = 35

5. 有兩個數字, 它們的和是27, 大的比小的兩倍大3, 請找出這兩個數.
----->假設這兩個數字分別是 X , Y:
1. X + Y = 27
2. X = 2Y + 3

(2Y + 3) + Y=27
3Y + 3 =27
3Y =24
Y =8

X + 8 = 27
X = 19

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