James A. answered • 02/10/14

Tutor

New to Wyzant
I teach how to understand the math, rather than how to do it

The key is the understand what the question is asking. Rewording the question, What number is six values less than 18? To put this question into equation form, we write

18 - 6 = ??

and the answer to this equation is 12.

18 - 6 = 12

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Another way to look at this is to ask the same question in a different form. What number, when you add 6 to it, will give you 18? Written as an equation,

?? + 6 = 18

Again, the solution to this equivalent question would be 12.

12 + 6 = 18

You can show the two questions/equations are equivalent by,

12 + 6 = 18

subtract 6 from both sides

12 + 6 - 6 = 18 - 6

the +6 and -6 on the left cancel out to zero

12 = 18 - 6

which is the same as 18 - 6 = 12

18 - 6 = 12