Give the Examples in Real World of Proportions?

Proportions can be used in cooking. For example, the following is a set of ingredients for a pasta called "Spaghetti All' Amatriciana." It usually makes enough for four people:
1 pound of spaghetti
1 (approx. 28 oz.) large can whole peeled tomatoes, pureed in processor, or crushed tomatoes
1 pound (16 oz.) slab bacon, diced into small cubes
1 small onion, chopped
1 small cayenne pepper, split Salt to taste

This is how you convert the amount of spaghetti to serve three people:
Step 1: Set up a proportion such that the ratio is the amount of food over the number of servings.

Step 2: Cross multiply.
3 pounds spaghetti = 4x

Step 3: Solve for x. (Divide both sides by 4.)

Follow the same steps for each ingredient. In the end, you have a recipe for "Spaghetti All Amatrician" that serves three people.