Huzefa K. answered • 04/23/14
Tutor
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Math Teacher|Michigan + Northwestern Law|Perfect Score Math ACT + SAT
Sure, you need to solve this algebraically by isolating r. So:
-52 = 4(7 + 5r)
-52 = 28 + 20r
-80 = 20r
r = -4
Lupita M.
how did you get -80?
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04/24/14
Huzefa K.
tutor
Hi Lupita,
I will break it down for you:
We start with -52 = 4(7 + 5r)
In order to find the value of r, you need to isolate r. That means you have to get it on one side of the equation by itself. The way you do that is by moving numbers around. The first step was multiplying 4 times 7 and 5r:
-52 = 28 + 20r
The next step is to move that 28 to the other side so that r can be by itself. How do you do that? Well, you can subtract 28 from the right side because 28 - 28 = 0.
But the problem with that is subtracting 28 changes the equation. So, to keep things balanced, you must subtract 28 from both sides:
-52 - 28 = 28 + 20r - 28
Which gives you:
-80 = 20r
Finally, you need to get rid of the 20 in front of the r; you do this by dividing by 20:
-80/20 = 20r/20
-4 = r
Report
04/24/14
Lupita M.
04/24/14