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I have been trying to solve this age problem: A boy's sister is 3 years younger than him. His father is 26 years older than the boy. Four years ago the father's age was 3 times the sum of the two children's age. Find the present ages of the father and his children.
Let boy's current age be B
Then sister's is: B - 3
Father's is: B + 26
We then get:
B + 26 - 4 = 3(B - 4 + B - 3 - 4)
B + 22 = 3(2B - 11)
B + 22 = 6B - 33
B - 6B = - 33 - 22
- 5B = - 55
B, or boy's current age =
, or 
You should now be able to find the sister's and the father's ages.