Question 1199205
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To work a problem like this, I encourage students to think informally, using the concept of slope as rise over run.  A student can get a better understanding of HOW he is solving the problem by doing that, instead of plugging numbers and variables into the formal formula for finding the slope between two points.<br>
In this problem, the two points are (R,2) and (5,3).
The rise is from 2 to 3, a difference of 1.
If the slope (rise over run) is 1/2 and the rise is 1, then the run must be 2.
If the run from R to 5 is 2, then R must be 5-2=3.<br>
ANSWER: R is 3<br>