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Unit fractions: numerator and denominator

Around age 8 · Usually taught in ⁨Year 2⁩ · Free

Aprende

  1. A whole pizza is 1 whole. If you cut it into 3 equal parts, each part is one third. One third is written .

    : 1 of 3 equal parts

  2. The line between the two numbers is the fraction bar. The bottom number is the denominator: it tells you how many equal parts the whole is divided into. The top number is the numerator: it tells you how many parts you take.

    When the numerator is 1, the fraction is called a unit fraction: you take 1 part. You already know and . Now you can also read (one third), (one fifth), (one sixth), (one eighth) and (one tenth).

    The name of the parts comes from the denominator. With 5 equal parts you get fifths. With 8 equal parts you get eighths.

    Be careful! The parts must be equal. If one part is bigger than another, they are not thirds or fifths.

    You can also look at a group of counters. Here there are 5 counters and 1 is shaded. That is of the counters.

    : 1 of 5 counters

  3. 3 thirds make 1 whole. 5 fifths make 1 whole. 8 eighths also make 1 whole.

    You can also take more than 1 part. Here the whole has 8 equal parts and you take 3. That is 3 parts of . It is written and read three eighths.

    : 3 parts of

Worked examples

Ejemplo 1

Julie cuts a pizza into 5 equal parts. She eats 1 part. What fraction of the pizza does she eat?

  1. Count the equal parts of the pizza: there are 5. That number goes at the bottom.
  2. Count the parts Julie eats: it is 1. That number goes at the top.
  3. 1 of 5 equal parts is one fifth.

Julie eats of the pizza.

¡Ojo! Many people write here, because they count the 4 parts that are left. The total number of equal parts always goes at the bottom: 5.

Common mistake

Ejemplo 2

Gus paints 3 of the 8 equal parts of a wall in Mara’s shop. What fraction of the wall does he paint?

  1. Count the equal parts of the wall: there are 8. That number goes at the bottom.
  2. Count the painted parts: there are 3. That number goes at the top.
  3. 3 parts of make . It is read three eighths.

Gus paints of the wall.

¡Ojo! Many people write here, because they count the 5 parts that are not painted. The total number of equal parts goes at the bottom: 8.

Common mistake

Ejemplo 3

Mara has a ribbon cut into 3 equal parts. How many thirds make the whole ribbon?

  1. Each part of the ribbon is one third: .
  2. Count the parts: there are 3.
  3. 3 thirds make the whole ribbon: 1 whole.

3 thirds make 1 whole.

¡Ojo! Many people answer 2 here, because they count the 2 cuts. You have to count the parts: there are 3.

Common mistake

Un reto para pensar

Draw a circle and a rectangle, both divided into 5 equal parts. Shade any parts you like and write the fraction for each drawing. How many different fractions can you write?

Practica

Rondas de 10 preguntas. Elige el nivel:

Next topic: Fracción de una cantidad (1/3 de 12; 3/4 de 20) →