This is a twenty dollar bill. This is an one liter bottle. This is a one thousand page book. I am a 32 year old english teacher. This is a 120 grams wooden bird. You probably already know that we use adjectives to describe nouns. For example, this is a big bag of pasta. The adjective "big" describes the noun "bag of pasta". This is a heavy book. The adjective "heavy" describes the noun "book". This is an empty bottle. The adjective "empty" describes the noun "bottle". But today we are going to learn about a different way to describe nouns. We are going to use a number and a noun instead of an adjective. This is a twenty dollar bill. We have the number "20" with the noun "dollar", and they are connected with a hyphen together, these describe the other noun bill. Twenty dollar works like an adjective to tell us that this bill is worth twenty dollar. This is a one liter bottle. We have the number one with the noun liter, and they are connected with a hyphen together, these describe the other noun bottle. One hyphen liter works like an adjective to tell us that this bottle has a volume of one liter. This is a 500 grams bag of pasta. We have the number 500 with the noun gram, and they are connected with a hyphen together. These describe the other noun bag of pasta. 500 grams works like an adjective to tell us that this bag of pasta weighs 500 grams. And you've probably noticed that the word after the hyphen does not have an "s" on the end. This is because it's not working as a regular noun. It's working as part of a compound adjective. So we don't need to add "s" on the end the way that we normally do with regular nouns. Let's look-at a few more examples. She has a two bedroom apartment. That means that her apartment has two bedrooms. This is an eight story building. That means that this building is eight stories tall. Nathan has a seven year old daughter. That means that he has a daughter who is seven years old.