Exercise 39 Page 9

Looking at the erroneous solution, we can see that the mistake made was related to whether - 0.8 should be added or subtracted from both sides of the equation. The critical mistake was that - 0.8 was added to both sides rather than being subtracted. Incorrect:r=12.6 + (- 0.8) Correct:r=12.6 - (- 0.8) One way to avoid this mistake would be to apply the Commutative Property of Addition to rearrange the terms on the left-hand side of the equation. See our correct solution below for an example.