We want to multiply
by
, and simplify.
The first thing we do in this type of problems, is factorize as much as possible, and see what cancels out.
can be factored into (r+2)(r+5) as 2 and 5 are two numbers whose sum is 7, and product is 10.
Similarly
can be factoredinto (r-10)(r+5) as -10 and 5 are two numbers whose sum is -5, and product is -50.
Last, (3r-30) can be factored as 3(r-10).
Thus the product is equal to:
,
so canceling all equal terms in the numerator and denominator we are left with
r+2.
Answer: A) r+2
mm = millimeters
m = meters
km = kilometers
So the distance is roughly 2, 500 miles so 4000km would be closer than the 3 measurements.