Lesson 10 The Numbers in Subtraction

- Let’s subtract fractions from whole numbers.

Warm-up Number Talk: Groups of Twelfths

Find the value of each expression mentally.

$2 \times \frac{3}{12}$
$6 \times \frac{3}{12}$
$12 \times \frac{3}{12}$
$12 \times \frac{30}{12}$

Activity 1 What’s Left?

Problem 1

A pitcher contains 3 cups of watermelon juice.

How many cups will be left in the pitcher if we pour each of the following amounts from the full amount?

image of a measuring cup, red liquid up to 3 cups line

$\frac{1}{4}$ cup
$\frac{5}{4}$ cups
$1 \frac{1}{4}$ cups
$2 \frac{2}{4}$ cups

Problem 2

A second pitcher contains 4 cups of water. How many cups will be left in that pitcher if we pour each of the following amounts from the full amount?

Explain or show your reasoning. Use diagrams or equations, if they are helpful.

$\frac{1}{3}$ cup
$\frac{5}{3}$ cups
$2 \frac{2}{3}$ cups

Activity 2 Card Sort: Twelfths

Problem 1

Sort the cards from your teacher into two groups. Record your sorted expressions. Be prepared to explain why the cards in each group belong together.

Problem 2

Find the value of each difference. Show your reasoning.

$1 - \frac{5}{8}$
$2 - \frac{7}{8}$
$3 - \frac{9}{8}$

Practice Problem

Problem 1

Show two different ways to find the difference: $2 - \frac{3}{4}$