數學題...用算式回答....20點20點20點20點20點20點急急急急急

[匿名]

2008-08-31 8:46 pm

1. Raymond spent 13/75(七十五分之十三) of his money on a book and spent 21/31(三十一分之二十一) of the remainder on a watch.He then had $120 left .How much money did he have at first??

2. 2X-5 ÷3=1.8 X=??

Solve the following equations

3.a. 6(X+2)=42
X=?

b. 4(X-0.4)-2=11.2

c.32-2X=18

d. 3/5(五分三)X-3=12

e. 8y-2=2y+34

f.y+3/4y=28

4. John is heavier than Mary. If their total weight is 82kg,find the weight of Mary.
Let Mary's weight be Y kg.
___________________+__________________=__________________

5.a. The sum of three consecutive(連續) numbers is 48. find the numbers.

(b)The sum of two consecutive even numbers is 86. find the numbers.

6.The length of rectangle is 3 times its width , and the perimeter is 24cm .Find the area of the rectangle.

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回答 (1)

yiuyiu

2008-09-01 2:14 am

✔ 最佳答案

1. Let X be the money he had at first
X - (X * 13/75) - {[X - (X * 13/75)] * 21/31] = 120
62X / 75 - 42X / 75 = 120
20X / 75 = 120
20X = 9000
X = 450

2. 先乘除後加減的做法為:
2X- (5 ÷ 3) = 1.8
2X = 1.8 + 5/3
2X = 1.8 + 1.67 (in 2 d.p) --- 要小數點後兩個位
X = 3.47 / 2
X = 1.735

唔知你條式有無打漏咗個括號呢，因為做法唔同:
(2X-5) ÷3=1.8
(2X-5) = 5.4
2X = 10.4
X = 5.2

3(a) 6(X+2)=42
6X + 12 = 42
6X = 30
X = 5

(b) 4(X-0.4)-2=11.2
4X - 1.6 -2 = 11.2
4X = 14.8
X = 3.7

(c) 32-2X=18
-2X = -14
X = 7

(d) 3/5X-3=12
3X - 15 = 12 * 5
3X -15 = 60
3X = 75
X = 25

(e) 8y-2=2y+34
8y-2y = 34 +2
6y= 36
y = 6

(f) y+3/4y=28
(4y + 3y)/4 = 28
7y = 112
y = 16

4. 條題目無講 John 重過 Mary 幾多kg呢?
Let X be the kg of John heavier than Mary

Y + (Y+X) = 82
2Y + X = 82

5.(a) Let X be the biggest number of the three consecutive numbers,
X + (X-1) + (X-2) = 48
3X -1 -2 = 48
3X = 51
X = 17
The three consecutive numbers are 17,16,15

(b) Let Y be the biggest number of the two consecutive even numbers
Y + (Y-2) = 86
2Y = 88
Y = 44
the two consecutive even numbers are 44 and 42

6. Let X be the width of the rectangle, and the length is 3X
(X + 3X) * 2 = 24
4X = 12
X = 3

The width of the rectangle is 3 cm and the length is 12 cm
The area of the rectangle is (3 * 12) cm(2次方) = 36 cm(2次方)

參考: ME

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