Los cardinal numbers y ordinal numbers tienen usos muy diferentes en inglés. A continuación encontrarás una explicación organizada.

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When to Use Cardinal Numbers

Cardinal numbers tell us how many (quantity).

Answer the question:

How many?

1. Counting

• One apple.
• Three books.
• Twenty students.

Examples

• I have two brothers.
• She bought five pencils.
• There are twenty people in the room.

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2. Age

• I am 30 years old.
• She is 12 years old.

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3. Phone Numbers

• My phone number is 555-123-4567.

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4. Prices

• It costs $15.
• The book is 20 dollars.

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5. Time

• It’s three o’clock.
• The meeting starts at 8:30.

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6. Dates (the Year)

• I was born in 1998.
• The company was founded in 2020.

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7. Measurements

• The table is two meters long.
• He weighs 80 kilograms.

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8. Math

• Three plus four equals seven.
• Ten divided by two equals five.

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9. Quantity

• I need six eggs.
• We have ten minutes.

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Cardinal Numbers

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When to Use Ordinal Numbers

Ordinal numbers tell us the position or order of something.

Answer the question:

Which one?

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1. Dates

One of the most common uses.

• July 4th
• December 25th
• October 31st

Examples

• My birthday is on May 15th.
• Christmas is on December 25th.

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2. Ranking

• She finished first.
• He came second.
• They finished third.

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3. Floors in Buildings

• I live on the third floor.
• The office is on the fifth floor.

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4. Sequence or Order

• Read the first chapter.
• Answer the second question.
• Open the third file.

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5. Birthdays and Anniversaries

• Today is my 21st birthday.
• They celebrated their 10th anniversary.

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6. Competitions

• First place
• Second place
• Third place

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7. Instructions

• First, open the book.
• Second, read the text.
• Third, answer the questions.

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8. Centuries

• The 21st century
• The 19th century

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9. Numbered Events

• The 10th Olympic Games.
• The 5th meeting.

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Ordinal Number Rules

• 1 → 1st (First)
• 2 → 2nd (Second)
• 3 → 3rd (Third)
• 4 → 4th (Fourth)
• Most numbers use -th: 4th, 5th, 6th, 7th, 8th, 9th, 10th…
• Numbers ending in 1 use st: 21st, 31st, 41st…
• Numbers ending in 2 use nd: 22nd, 32nd, 42nd…
• Numbers ending in 3 use rd: 23rd, 33rd, 43rd…
• Exceptions: 11th, 12th, and 13th always use th.