The sum of the initial and final velocity is divided by 2 to find the average. The average velocity calculator uses the formula that shows the average velocity (v) equals the sum of the final velocity (v) and the initial velocity (u), divided by 2.
so 18km is equivalsnt to 18000m and 3 hours is 180 minutes which is 10800 seconds. you can put it into a fraction which would be 18000/10800. we can turn this into 18000 ÷ 10800 and that equals 1.66666.....(recurring)
