When it comes to ordinal numbers, it is important to understand the correct usage of suffixes such as “-th” and “-st”. In the case of “91th” and “91st”, the correct option is “91st”. The reason for this is that the suffix “-st” is used to indicate the position of a number in an ordered sequence. Let’s delve deeper into the explanation and explore some examples to solidify our understanding.

Ordinal numbers are used to denote the position of something in a series or an ordered list. They are different from cardinal numbers, which are used to indicate quantity or number. In written form, ordinal numbers often include a suffix at the end, such as “-th”, “-st”, “-nd”, or “-rd”. These suffixes add a sense of order to the number, indicating its position in a sequence.

In the case of the number 91, we would use the suffix “-st” to form the ordinal number “91st”. This is because “91” is in the numerical position of the first in a series. The suffix “-st” is the appropriate choice for the first position, while the suffixes “-th”, “-nd”, and “-rd” are used for other positions.

To further illustrate this point, let’s look at some examples:

1. The 21st century is known for its rapid technological advancements.

2. She finished in 2nd place in the race.

3. He was the 3rd person to arrive at the party.

In these examples, we can see the correct usage of the ordinal suffixes. The 21st century denotes the first position in the series of centuries, while 2nd and 3rd indicate the second and third positions in the race and party, respectively.

Now, you might be wondering why we don’t use the suffix “-th” for all ordinal numbers. The suffix “-th” is actually used for numbers other than 1, 2, and 3. When a number ends in 1, we use “-st”, when it ends in 2, we use “-nd”, and when it ends in 3, we use “-rd”. For all other numbers, we use the suffix “-th”.

Let’s consider some additional examples:

1. I live on the 10th floor of the apartment building.

2. This is my 15th attempt at solving this puzzle.

3. The 50th anniversary celebration was a grand affair.

In these examples, we can observe the correct application of the respective suffixes. “10th” indicates the tenth position, “15th” denotes the fifteenth position, and “50th” implies the fiftieth position.

In conclusion, the correct option between “91th” and “91st” is “91st”. When using ordinal numbers, we need to pay attention to the appropriate suffixes. In the case of the number 91, we employ the suffix “-st” to denote its position in an ordered sequence. By understanding the rules behind ordinal numbers and their suffixes, we can effectively communicate and express numerical positions accurately in our writing and conversations.