Tim solved the question: X + 7 = -15
His steps were as follows: X + 7 = -15, add seven to both sides, X = -8, (-8) + 7 = -1
When he checked back, his solution didn’t work
What was his error?
Tim's error was in the step: "X = -8, (-8) + 7 = -1".
The correct step should be: "X = -8, (-8) + 7 = -1 + 7 = 6".
Tim incorrectly added 7 to -8, resulting in -1 instead of the correct answer of 6.
Tim's error was in the step where he calculated the value of X after adding seven to both sides. He incorrectly calculated (-8) + 7 to be -1 instead of -15, which is the correct value that satisfies the equation.
Tim's error occurred when he simplified the equation (-8) + 7 = -1. Let's go through the steps to solve the equation and see where the error occurred.
The original equation is X + 7 = -15.
Tim correctly added seven to both sides of the equation, which gives us X = -8. This is the correct value for X.
However, when Tim checked his solution by substituting X = -8 back into the equation, he made a mistake. Instead of (-8) + 7, he incorrectly simplified it to (-8) + 7 = -1.
The correct calculation should be (-8) + 7 = -8 + 7 = -1. Therefore, Tim made an error when he mistakenly equated (-8) + 7 to -1 instead of -8 + 7.