twelve decreased by twice a number is -7. find the number

Question

need help

Answer 1

Let x = the unknown number.  Twelve (12) decreased by (minus) twice a number (2x) is (=) -7:

 

12 - 2x = -7

12 = -7 + 2x          [Added 2x to both sides]

12 + 7 = 2x           [Added 7 to both sides]

19 = 2x                 [Divide both sides by 2]

 

19/2 = x

 

Check:

12 - 2x = -7

 

Plug 19/2 in for x:

 

12 - 2(19/2) = -7

12 - 19 = -7

-7 = -7

Check!

Answer 2

For this, you just need to know how to translate problems like this. "Decreased by" means "minus", "twice" means "multiply by 2", "a number" just means "variable", and "is" stands for "equals". So translated, the problem becomes:

 

12 - 2x = -7

 

So now solve for "the number", or x:

 

12 - 2x = -7

-2x = -19

x = 19/2