Jennifer H. answered • 06/20/19
Certified HS/college science teacher with a passion for biology
According to the units km/h, the formula for speed is distance/time, that is distance divided by time. But as you can also see from the units, the time given is in minutes, not hours. In order to combine these numbers, the units have to match, so your first step is to convert 2 minutes to hours. 2 is less than 60 (the number of minutes in an hour), so your answer will be a decimal number less than one, specifically, the answer to 2/60, which = .033 repeating. We'll go ahead and round that to .03 hours (both given numbers only have one significant figure, so this one has to as well) and place it, and the given speed, 20 km/h, into the speed equation. The speed equation, like you may suspect, is s = d/t (speed = distance/time). At this point, you can plug in the numbers for speed and time into the equation and solve for the unknown variable distance, or you can rearrange the formula to solve for distance, then plug in the known numbers. I'll show you both ways.
plug in numbers and solve for distance:
20 km/h = d/0.03 h (with units)
20 = d/0.03 (without units)
multiply both sides by 0.03. This cancels the 0.03 in the denominator on the right and gives you .6 on the left. Therefore 0.6 = d, or turn it around and d = 0.6 km
rearrange formula and plug in numbers:
s = d/t, but if you multiply both sides by t to get it out of the denominator, you're left with d = st, which means distance = speed times time.
d = 20 x 0.03
therefore d = 0.6 km
Why are the units of distance kilometers? because that is what they are in the number given for speed,
20 km/h
