Form 1 Maths(最佳解答者have 40分)

A man is 42 years old and his son is 4 now. In how many years later will the father be as 3 times as old as his son?

Solution 1:
Let x be the years after the father's age will be 3 times as old as his son.
3(4+x)=42+x
12+3x=42+x
3x-x=42-12
2x=30
x=15

So, 15 years later, the father's age will be as 3 times as old as his son.


Solution 2:
Let x be the years after the father's age be 3 times as old as his son.
x+4=(42+x)/3
x+4=14+x/3
x-x/3=14-4
2x/3=10
2x=30
x=15

So, 15 years later, the father's age will be 3 times as old as his son.

A man is 42 years old and his son is 4 now. In how many years later will the father be as 3 times as old as his son?

Let x be the time of the father being as 3 times as old as his son

42+x=3(4+x)

42+x=12+3x

42-12=3x-x

2x=30

x=15

In 15 years later will the father be as 3 times as old as his son

Answer:
Let x be the years the father will be 3 times as old as his son :

42 + x = 3 (4+x)
42 + x = 12 + 3x
3x + x = 42 - 12
2x = 30
x = 15

There the father will be 3 times as old as his son in 15 years.

42 + x/3 = 4 + x

42 + x = 3(4+x)

42+ x = 12 + 3x

42 -12 = 3x - x

30 = 2x

15 = x

x = 15

Let x be the year after the father's age will be as 3 times as old as his son .
42+x / 4+x =3
42+x =12+3x
42-12= 3x-x
30 = 2x
x = 15
∴ The father's age will be as 3 times as old as his son after 15 years.

Let x be the year later:

42+x = (4+x) X3

42-12+x = 3x

30= 2x

x = 15

Shall we let x years later, the age of the father is 3 times as the son's.

42+x = 3(4+x)
42+x = 12+3X
2x = 30
x =15

Therefore, 15 years later, the age of the father is 3 times as the son's.
And by the time, the father will be 57 and the son will be 19.

Let x be the years the father will be 3 times as old as his son :

42 + x = 3 (4+x)
42 + x = 12 + 3x
3x + x = 42 - 12
2x = 30
x = 15

There the father will be 3 times as old as his son in 15 years.

2007-01-07 15:23:34 補充：
oops, it should be THEREFORE.

2007-01-07 15:25:22 補充：
o and, it shold be 3x-x. sorry

Let x years later will that the father be as 3 times as old as his son,

42 + x/3 = 4 + x

42 + x = 3(4+x)

42+ x = 12 + 3x

42 -12 = 3x - x

30 = 2x

15 = x

x = 15

hence,the required answer is 15 years

hope its help:)

Let x years later will the father be as 3 times as old as his son

42 + x / 3 = 4 + x
42 + x = 3(4+x)
42+ x = 12 +3x
42-12 = 3x - x
30 = 2X
15 = x
x = 15

15 years later will the father be as 3 times as old as his son