Answer: Choice A
Reasoning:
Every direct proportional function always goes through the origin (0,0). In other words, the y intercept is always 0.
Choices B, C, and D can be ruled out because their y intercepts are nonzero (eg: choice D has a y intercept of 10).
With choice A, the point (0,0) is on the graph. So far, so good. Notice that dividing each pair of nonzero x,y values leads to the same result.
- column 3: y/x = 50/5 = 10
- column 4: y/x = 100/10 = 10
This suggests that the constant of proportionality is 10, and that the equation for table A is y = 10x. Any direct proportion equation is of the form y = kx, with k being the constant of proportionality. To find k, we can write k = y/x where x,y are nonzero.
