1 Maths Question (Linear Equation in Two Unknows)

2007-02-26 1:15 am

The Question :
Ten years ago, a father's age was four times his son's. Ten years later, the father's age will be twice his son's. How old are they now?

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I know that it's very easy to think but hard to show it into a solution. Can anyone help me?

回答 (1)

sunny

2007-02-26 1:21 am

✔ 最佳答案

Ten years ago, a father's age was four times his son's. Ten years later, the father's age will be twice his son's. How old are they now?

Let the father's age now be a, the son's age now be b

a - 10 = 4( b - 10 )................(1)
a + 10 = 2( b + 10)................(2)

From (1),
a - 10 = 4b - 40
a = 4b - 30...........................(3)

From (2)
a + 10 = 2b + 20
a = 2b + 10............................(4)

Substitute (3) into (4)
4b - 30 = 2b + 10
2b = 40
b = 20 //

Substitue b = 20 into (4)
a = 40 + 10
a = 50 //

The father is 50 years old, the son is 20 years old

參考: me~

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