Question

Ella simplifies (3b+4r)+(-2b-r) and says the result is b+5r. What error did Ella make?

Answer 1

The correct answer is (D).
   (3b + 4r) + (-2b - r)       = (3b - 2b) + (4r - r)           = b + 3r
   not
 b + 5r
   * Ella added (4r + r) instead subtracting (4r - r), thus she got the wrong answer.

Answer 2

D is the answer.
3b+(-2b)= 1b (same as 3-2=1)
4r+(-r)= 3r (same as 4-1=3)
When you add a negative, you subtract.