Discussion
If 3x + 9 = 15, then x + 2 =
*This question is included in Nova Math - Diagnostic/Review:, question #1
| (A) | 2 |
| (B) | ... |
| (C) | ... |
| (D) | ... |
| (E) | ... |
| (F) | ... |
The solution is
Posted: 08/10/2013 05:33
I must be old. This is not how we learned math when I was a kid. I don't understand where the "subtract 1" came from. How did that enter the equation? If you divide 3 into both sides you'd either be left with x+9=5 or x+3=5... Neither of which would give you 4.... I'm hopeless.
Posted: 08/10/2013 17:28
Hi J Schmidt,
We divided by 3 and then subtracted 1 because that is probably the most efficient way to solve for the expression x + 2. However, we could solve the equation 3x + 9 = 15 for x and when done just add 2 to it, forming the expression x + 2. To that end, subtract 9 from both sides of the equation 3x + 9 = 15:
3x + 9 - 9 = 15 - 9
Reducing yields
3x = 6
Now, dividing by 3 yields
3x/3 = 6/3
or
x = 2
Finally, adding 2 to both sides of this equation to create the term x + 2 yields
x + 2 = 2 + 2
or
x + 2 = 4
Thus, the answer is (C).
We divided by 3 and then subtracted 1 because that is probably the most efficient way to solve for the expression x + 2. However, we could solve the equation 3x + 9 = 15 for x and when done just add 2 to it, forming the expression x + 2. To that end, subtract 9 from both sides of the equation 3x + 9 = 15:
3x + 9 - 9 = 15 - 9
Reducing yields
3x = 6
Now, dividing by 3 yields
3x/3 = 6/3
or
x = 2
Finally, adding 2 to both sides of this equation to create the term x + 2 yields
x + 2 = 2 + 2
or
x + 2 = 4
Thus, the answer is (C).
Posted: 08/10/2013 11:30
Mr Schmidt, you are younger than me, I can guarantee. Remember, we are solving for x+2, not x. Subtracting 1 enters into the equation because after dividing by 3, we were left with x+3, so in order to get x +2, we need to subtract by 1.