(a)A man is 14 years older than his son. Two years later, his age will be twice that of his son. Find the age of his son now.
b-c是方程式
(b) 5 times a number is greater than 3 times the number by 4. Find the number . Solution: let x be the number.
(c) The length of a rectangle is 3 cm longer than its width. The perimeter of the
rectangle is 30 cm. Find the length of the rectangle. Solytion : Let x cm be the length of the rectangle.
呢幾條題來自Train Up MATHEMATICS 1 (S.1-S.2)
maths 我唔識 help plz !!
2007-07-26 11:44 pm
回答 (3)
2007-07-26 11:54 pm
✔ 最佳答案
(a)Let the age of his son be X now. Then the age of the man is X + 14.
Two years later, age of the son is X + 2 while age of the man is (X + 2) + 14. Age of the man is twice of his son. This means:
(X + 2) + 14 = 2 (X + 2)
X + 16 = 2 X + 4
X = 12
(b)
Let x be the number.
5 x – 3 x = 4
2 x = 4
x = 2
(c)
Let x cm be the length of the rectangle.
Width = x – 3
Perimeter = 2 ( x + Width) = 2 ( x + x – 3) = 2 (2 x – 3) = 4 x – 6 = 30
4 x = 36
x = 9
2007-07-26 11:56 pm
a.
Let x be the age of his son.
(x + 14)+ 2 = 2x
x + 16 = 2x
16 = 2x-x
x = 16
His son is 16 years old.
b.
Let x be the number.
5x = 3x + 4
5x - 3x = 4
2x = 4
x = 2
The number is 2.
c.
Let x cm be the length of the rectangle.
2 ( x - 3 + x ) = 30
x - 3 + x = 15
2x - 3 = 15
2x = 18
x = 9
The length of the rectangle is 9 cm.
Let x be the age of his son.
(x + 14)+ 2 = 2x
x + 16 = 2x
16 = 2x-x
x = 16
His son is 16 years old.
b.
Let x be the number.
5x = 3x + 4
5x - 3x = 4
2x = 4
x = 2
The number is 2.
c.
Let x cm be the length of the rectangle.
2 ( x - 3 + x ) = 30
x - 3 + x = 15
2x - 3 = 15
2x = 18
x = 9
The length of the rectangle is 9 cm.
參考: My mathematical knowledge
2007-07-26 11:55 pm
(a) x = y + 14
x+2 = 2 (y+2)
x=2y+ 2
y + 14 = 2y + 2
y = 12
x = 26
(b)5x = 4 + 3x
2x = 4
x = 2
(c) (x + (x+3)) x 2 = 30
2x + 3 = 15
2x = 12
x=6
so, width is 6cm, length is 9cm
x+2 = 2 (y+2)
x=2y+ 2
y + 14 = 2y + 2
y = 12
x = 26
(b)5x = 4 + 3x
2x = 4
x = 2
(c) (x + (x+3)) x 2 = 30
2x + 3 = 15
2x = 12
x=6
so, width is 6cm, length is 9cm
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