Answers (2)
Given speed: 8km/30sec
A conversion factor is a fraction equal to 1. You are given that one hour equals 60 minutes so you can write that as hr/60min=1 or 60min/hr=1 whichever works for you and drop it into an equation anywhere and it only changes the units.
ANSWER = You write this first so it looks like you know what you are doing. That gives you a bit of time to figure out what to do next.
ANSWER = 8km/30sec x mile/0.621km x 3600sec/hr
Ok, now we check everything. This is called sanity check and it is especially important in chemistry and physics where you might have a dozen or so conversions in a single equation. We have km above the line and again below, so that cancels. We have sec below the line and again above so that cancels. We have mile above the line and that appears in the answer. We have hr below the line and that appears in the answer. When you are sure everything is right, multiply all the numbers above the line and divide by all the numbers below.
ANSWER = 8km/30sec x mile/0.621km x 3600sec/hr = 1545.894 mph