Grado 5Multiplying and Dividing Fractions5.NF.B.3

A Fraction Is a Division

3/4 means 3 ÷ 4: three things shared by four.

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Esta lección aún no está traducida. Por ahora se muestra en inglés; la versión en español está en camino.

You know division with remainders and mixed numbers. Here is a link between them: the fraction bar is a division sign. $\frac{3}{4}$ means $3 \div 4$.

Idea clave

$\frac{a}{b} = a \div b$. Sharing $a$ wholes equally among $b$ people gives each person $\frac{a}{b}$ of a whole, even when $a$ is smaller than $b$.

Por qué funciona

Share 3 pizzas among 4 people. Cut each pizza into 4 equal slices. Each person takes one slice from each pizza: 3 slices, each $\frac{1}{4}$ of a pizza. So each person gets $\frac{3}{4}$, and $3 \div 4 = \frac{3}{4}$.
Three pizzas (one bar each), each cut into fourths. One person's share is one fourth of each pizza: $\frac{1}{4} + \frac{1}{4} + \frac{1}{4} = \frac{3}{4}$ of a pizza.

Worked examples

Ejemplo resuelto: A smaller number divided by a larger one

Write $3 \div 4$ as a fraction.
  1. The number being divided goes on top: $\frac{3}{4}$.
  2. Check: 4 shares of $\frac{3}{4}$ make $\frac{12}{4} = 3$.

Respuesta: $\frac{3}{4}$

Ejemplo resuelto: More than one whole each

5 people share 7 pounds of clay. How much does each get?
  1. $7 \div 5 = \frac{7}{5}$.
  2. As a mixed number: 5 goes into 7 once with 2 left, and the 2 are shared too: $1\frac{2}{5}$.

Respuesta: $1\frac{2}{5}$ pounds

Ejemplo resuelto: Between which whole numbers?

Between which two whole numbers is $\frac{17}{5}$?
  1. $\frac{17}{5} = 17 \div 5$.
  2. $5 \times 3 = 15$ and $5 \times 4 = 20$, so the answer is 3 with 2 left over: $3\frac{2}{5}$.

Respuesta: between 3 and 4

Error común

Believing a smaller number cannot be divided by a larger one, so $3 \div 4$ “can't be done” or is 0 R 3. It can: each share is just less than 1. Check by multiplying: $4 \times \frac{3}{4} = 3$.

Práctica

Apruebas con 3 respuestas correctas, las 2 últimas seguidas. Cada respuesta correcta da 2 XP.

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Fuentes y lecturas

  • OpenStax Prealgebra 2e, 4.1 Visualize Fractions
  • Common Core State Standards for Mathematics, 5.NF.B.3: interpret a fraction as division of the numerator by the denominator