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I am half the age of my dad plus four but I know that my dad is eight years older than my mum and my mum gave birth to me
at the age of twenty eight. What is my age?
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The first equation is
I = (1) (I is "my age", D is dad's age)
The second equation is
D - I = 28 + 8. (2) (My dad is 28+8 years older than me).
You can rewrite equations (1) and (2) in the form
2I = D + 8 (1')
D - I = 36. (2')
From (2'), express D = 36 + I and then substitute it into (1') replacing D. You will get
2I = (36+I) + 8 ----> 2I = I + 44 ----> I = 44.
There is a bunch of lessons on age word problems
- Age problems and their solutions
- A fresh formulation of a traditional age problem
- Really intricate age word problem
- Selected age word problems from the archive
in this site.
Read them and become an expert in solving age problems.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this online textbook under the topic "Age word problems".