As we know Speed= Distance/time
If we represent speed by S and distance by D and time by T,
If we keep Distance Constant
then Speed is inversely proportional to time.
S will be inversely proportional to T.If time increases it means speed has decreased to cover same amount of distance.
Or time has decreased it means speed has increased to cover same amount of distance.
Now keeping time fixed , if we increase the speed of an object we can cover more distance or if we decrease speed, distance traveled will be less.
This shows that speed is directly proportional to Distance.
Now coming to next example of number of workers and number of days and their working hours
if number of workers increases keeping hours fixed in a day their working days will get reduced.
Or
If Working days increases keeping hours fixed Number of worker decreases.
Keeping Workers fixed, work for more hours number of days will get reduced.
If same amount of worker works for less hours number of days will get increased.
This was the case of inverse proportion.
Suppose i solve a question in 5 minutes . If i sit for more hours more number of question will be solved.
As you can see in this example keeping time constant
Number of question solved is directly proportional to how many hours i sit to solve question.