Explain why it is important to line up decimal numbers by their place value when you add or subtract them

it is important because it make the problem simpler to solve, and you're more likely to make less mistakes because you know the place value for each number, and so that you don't mistakenly add numbers with different values.

in short, because you're more likely to solve the problem correctly if you do.

mrbilldoesmath!

answer: a parabola

steps:

(x-1)(x+4)   = x(x+4) - 1(x+4) = (x^2 + 4x) - (x+4)

                = x^2 +4x -x -4   = x^2 +3x -4

which is a parabola

mrb