Question 1161810: Twice the difference of a number and 9 is equal to three times the sum of the number and 4. Find the number
Found 3 solutions by ikleyn, josgarithmetic, greenestamps:
Answer by ikleyn(52832)   (Show Source):
You can put this solution on YOUR website! .
2*(x - 9) = 3*(x+4)
2x - 18 = 3x + 12
-12 - 18 = 3x - 2x
x = -30. ANSWER
Solved.
----------------
Regarding the post by @josgarithmetic, giving two solutions/answers 6 and -30,
keep in mind, that his answer 6 is wrong.
Answer by josgarithmetic(39623)  (Show Source):
Answer by greenestamps(13203)  (Show Source):
You can put this solution on YOUR website!
The expressions are linear; there will not be two different answers.
The problem with the solution by tutor @josgaritihmetic is that it uses two different interpretations of "the difference of a and b".
In everyday language, a difference is nearly always assumed to be a positive number. For example, if a man is 40 and his wife is 35, then the difference of the man's age and the wife's age is 5 years, and the difference of the wife's age and the man's age is 5 years.
But in mathematics, you can't have two different interpretations of "difference".
Mathematically, the difference of the man's age and his wife's age is 5; the difference of the wife's age and the man's age is -5.
In other words, mathematically, the difference of A and B is ALWAYS A-B; it is NEVER B-A.
|
|
|
