Expert: Scott A Wilson - 6/22/2010

Question
Which group of points are all on the line y =.5x + 6?
A:(–2, 5); (2, 5); (4, 4)
B:(–2, 5); (2, 7); (4, 8)
C:(–2, 7); (2, 7); (4, 4)
D:(–2, 7); (2, 5); (4, 8)

Answer
Looking at the answer, I would compute 0.5x + 6 for x equal to -2, 2, and 4.
That looks like it would give, for y, -1+6, 1+6, and 2+6.
Compute those y values and it can be determined which answer is right.

Also, it could be noted that since the x's differ by 4 and then 2,
the y's should differ by 2 and then 1.  So to the first y choice, add 2.

For A, the 1st y is 5, so the next should be 7, bt it is 5, so that's not the answer.
For C, the 1st y is 7, so the next should be 9, but it is 7, so that's not the answer.
For D, for 1st, y is 7, so the next should be 9, but it is 5, so that's not the answer.

This leaves only B, and that should be checked out.
For x=-2, y = -2/2 + 6.  Now -2/2 is -1, and -1+6=5, and thats what's there for y.
For x=2, y = 2/2 + 6.  Now 2/2 is 1, and 1+6=7, and thats what's there for y.
For x=4, y = 4/2 + 6.  Now 4/2 is 2, and 2+6=8, and thats what's there for y.

Having done the check, it can be seen that this choice is the correct answer.