Question 1150830
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One clear way to set up the problem directly from the given information, as the other tutor did, is to let j be Jake's age, and so Mike's age is 2/3 of j.  Then form an equation that says the sum of their ages is 30 and solve the equation to find Jake's age.<br>
{{{j + (2/3)j = 30}}}
...<br>
Since many people (and not just beginning students) prefer to use a setup that avoids using fractions, here is an alternative method for solving the problem.<br>
"Mike is 2/3 of Jake's age"
-->  the ratio of their ages is 2:3
-->  let 2x be Mike's age and let 3x be Jake's age<br>
Now write and solve an equation that says the sum of their ages is 30:<br>
{{{2x+3x = 30}}}
{{{5x = 30}}}
{{{x = 6}}}<br>
The disadvantage to this method is that solving the equation doesn't directly give you the answer to the question.  The answer to the question is Jake's age, which is 3x = 18.<br>