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A is x years old. In 4 years time his brother B will be 3 times as old as him. Find the age of B in 4 years time.

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    $\begingroup$ What have you tried? See also this ratio problem. $\endgroup$ – Dietrich Burde Dec 2 '18 at 19:15
  • $\begingroup$ I have tried various approaches. But my teacher restricted me to solve it by algebra. $\endgroup$ – Wardah Dec 2 '18 at 19:18
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$x$ is A's age and let's call B's age $y$ at this point in time
Hint : In 4 years time A: is $x+4$ years old and B is $y+4$ years old
Solution

We know that B will be 3 times older than A in 4 years, aka $3*(x+4)=y+4$
Solving for $y$ : $y=3x+8$
In four years time B will be $y+4$ years old or aka $3x+8+4 = 3x+12$

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