Divide 100 by the number of meters the person or object travels in 1 second. For example, a velocity of 5m/s would become 100 ÷ 5 = 20. The quotient, in this case 20, is the number of seconds it will take for the person or object to travel 100 meters.
Check your solution by multiplying the quotient by the divisor, in this case 5. If you get 100 as the answer, you have correctly done the math. This step is especially important if you are not using a calculator.
Round to the appropriate place, if necessary. For example, if the average speed is 7 m/s, 100 ÷ 7 = 14.285714. Most stopwatches measure only to the nearest hundredth of a second, or two digits after the decimal. To round to the nearest hundredth, the digits to the left of the 8 stay the same, as in 14.2. Look at the digit to the right of the 8, in this case 5. If it is a 5 or greater, the 8 will round up to a 9. If it is a 4 or less, the 8 will remain the same. In this case, the quotient would round to 14.29, which is the number of seconds it will take for that object to traverse 100 meters.
Change the units to meters per second. There are 1000 meters in a kilometer, and 3600 seconds in an hour, so multiply the kilometers by 1000 and the hours by 3600 and rewrite as per the example given: 5km/h = 5000m/3600s.
Divide both meters and seconds by 3600. In this case, 5000m/3600s becomes 1.3888...m/s. Round to the nearest hundredth, as shown above in step 3 of the Meters per Second section. The solution in this case would be 1.39m/s.
Convert to 100 meter time by dividing 100 by the meters unit; in this case 100 ÷ 1.39 = 71.9424... seconds, which will round to 71.94s. This time can also be written as 1min:11.9s and is the amount of time it will take that person or object to traverse 100 meters. Double-check your division if necessary.