Lesson 6 of 10 · Grades 3 to 4
What division means
Division answers a sharing question. You can share a pile into a given number of equal groups, or you can find how many equal groups fit inside a pile. Both pictures use division, and both undo multiplication.
Sharing a pile equally
Division is the arithmetic of fair shares. You have a pile of something and a number of people or places to share it among. Division tells you how much each share gets. Twelve grapes shared among three children gives four grapes each. We write that as 12 ÷ 3 = 4.
The division sign asks a question: if the pile is split into that many equal groups, how big is one group? The key word is equal. Every share must be the same size, exactly as the groups in a multiplication must be the same size.
Making equal groups
There is a second way to read the same division. Instead of counting out shares, you can ask how many groups of a given size fit into the pile. Twelve grapes make three groups of four. The picture is the same; the question is different.
This second reading is useful for problems about packing. If 54 pencils are packed with 6 in each box, you are asking how many boxes of 6 fit into 54. The division 54 ÷ 6 = 9 answers it directly. Children who can move between the two pictures find division word problems much easier.
The names of the parts
Division has its own three names. The number being divided is the dividend. The number you divide by is the divisor. The answer is the quotient. In 12 ÷ 3 = 4, the dividend is 12, the divisor is 3 and the quotient is 4.
Notice how the three numbers line up with a multiplication fact: 12 ÷ 3 = 4 and 3 × 4 = 12. Division undoes multiplication, and multiplication undoes division. This back-and-forth relationship is the theme of the last lessons in this course.
Watch out for this
In a division story, decide what is known before you write the numbers. If you know the total and the number of groups, you find the group size. If you know the total and the group size, you find the number of groups. Writing the numbers in the wrong order gives the wrong picture, even when the division itself is correct.
Worked example
24 counters are shared equally among 6 children. How many counters does each child get?
Step 1: the story shares a pile equally, so use division. The pile has 24 counters and there are 6 groups.
Step 2: write 24 ÷ 6.
Step 3: ask how many counters go into each group. Six groups of 4 make 24, so each child gets 4.
Step 4: check with multiplication: 6 × 4 = 24. The product matches the number we started with.
Answer: 4 counters each.
Remember
- Division shares a total into equal groups.
- It can also ask how many equal groups fit inside a total.
- The dividend is shared, the divisor does the sharing, and the quotient is the answer.
- Division undoes multiplication.
Try it
Answer the five questions below. Work them out first, then open each answer to check.
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24 counters are shared equally into 4 groups. How many counters are in each group?
Show answer
6 counters. 24 ÷ 4 = 6.
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What is 30 ÷ 5?
Show answer
6. Five groups of 6 make 30.
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Which division undoes 6 × 7 = 42?
Show answer
42 ÷ 6 = 7, and also 42 ÷ 7 = 6. Both undo the multiplication.
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18 beads are shared equally into 9 groups. How many beads are in each group?
Show answer
2 beads. 18 ÷ 9 = 2.
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35 grapes are shared equally among 5 children. How many grapes does each child get?
Show answer
7 grapes. 35 ÷ 5 = 7.
Puzzle · Share the counters
Puzzle time
Eighteen counters are shared equally into 3 cups. How many counters land in each cup?
Show a hint
Find the number that makes 3 equal groups of 18. Which number times 3 equals 18?
Show the answer
Answer: 6. 18 ÷ 3 = 6, so each cup gets 6 counters. Check: 3 × 6 = 18. The trap answer 9 would only fill 2 cups.