.
You are given that "In 3 years the sum of their ages will be 83."
It means that NOW the sum of their ages is 83-3-3 = 77.
So, you have these two equations
C = D + 7, (1)
C + D = 77. (2)
In equation (2), replace "C" by (D+7), based on (1). You will get
(D+7) + D = 77 ====> 2D + 7 = 77 ====> 2D = 77-7 = 70 ====> D = = 35.
Thus Dan is 35 years old.
Then Cary is 35+7 = 42 years old.
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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
- Age problems for mental solution
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".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson
to your archive and use it when it is needed.