### Theory:

Let us see a situation where the systematic listing is needed.

Suppose you need to count the number of passengers in the crowded bus.

In that, some passengers are sitting, and some are standing. In this situation, we are unsure of the count that we made and sometimes we may count the same head more than once!

It isn't easy to make sure that our count would be correct.

Let us consider another situation with different seating arrangement of passengers.

In this situation, there are $$14$$ rows of seats in the bus and each seat is filled with $$2$$ passengers.

In here, it is easy to calculate the number of passengers in the bus.  It is simply $$14\times 2 = 28$$.

Let us consider another scenario where $$3$$ of seats are not filled by the passengers and $$2$$ of passengers are standing in the bus to get down at the next stop.

In this case, out of $$28$$ seats $$2$$ of the seats were not filled in and $$3$$ were standing.

Total number of passengers $$=$$ $$28-3+2$$ $$=$$ $$27$$.
From the above discussion, it can be concluded that 'The place in which the things are counted is fixed and arranged in some order, then counting is simple'. Thus it is recommended that the things should be in order if it is needed to be counted easily.