Question 53415
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What is -y + 10 = 25? I did:
-y + 10 = 25
    -25  -25
  -y = -15
-1(-y) = -1(-15)
    y = 15
Am I right?
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As @IKLEYN pointed out, the answer you came up with, and @consc198 agreed with: y = 15, is WRONG! 

You stated: What is -y + 10 = 25? I did:
                                  - y + 10 = 25
                                           -25  -25   <=== Here, you should've SUBTRACTED 10 from each side, instead of 25 
                                           - y = - 15 <=== This is where you went WRONG
                                   - y - 15 = 0 <=== This is what you should've had
                                         - 15 = y ---- ADDing y to each side              

A very EASY WAY is: 
                                 - y + 10 = 25
                                       -  10  - 10 <=== Subtracting 10 from each side, to ISOLATE the variable                                  
                                          - y = 15
                                          {{{highlight(y) = 15/(- 1) = highlight(- 15))}}}</font></font></font></b></pre>