WARM-UP
NEW CONCEPT
Stories about combining have an addition pattern. Stories about separating have a subtraction pattern. Stories about equal groups have a multiplication pattern. Here are three
“equal groups” stories:†
At Lincoln School there are 4 classes of fifth graders with 30 students in each class.
Altogether, how many students are in the four classes?
The coach separated the 48 players into 6 teams with the same number of players on each team. How many players were on each team?
Monifa raked up 28 bags of leaves. On each trip she could carry away 4 bags. How many trips did it take Monifa to carry away all the bags?
Facts Practice: 90 Division Facts (Test D or E) Mental Math:
Problem Solving:
3 ¥ 40 plus 3 ¥ 5 4 ¥ 45
120 + 70 210 + 35
Start with 5, ¥ 6, + 2, ÷ 4, + 1, ÷ 3† a.
c.
e.
g.
h.
b.
d.
f.
Count up and down by 25’s between 0 and 200.
Count up and down by 250’s between 0 and 2000.
The uppercase letter A encloses one area, B encloses two areas, and C does not enclose an area. List all the uppercase and lowercase letters that enclose at least one area.
4 ¥ 50 plus 4 ¥ 4 4 ¥ 54
560 – 200
†As a shorthand, we will use commas to separate operations to be performed sequentially from left to right. In this case, 5 ¥ 6 = 30, then 30 + 2 = 32, then 32 ÷ 4 = 8, then 8 + 1 = 9, then 9 ÷ 3 = 3. The answer is 3.
102 Saxon Math 6/5
There are three numbers in a completed “equal groups”
story—the number of groups, the number in each group, and the total number in all the groups. These numbers are related by multiplication. Here we show the multiplication pattern written two ways:
Number of groups ¥ number in each group = total
The number of groups is one factor, and the “in each”
number is the other factor. The total number in all groups is the product.
In an “equal groups” story problem, one of the numbers is missing. If the total is missing, we multiply to find the missing number. If the “in each” number or the number of groups is missing, we divide.
Example 1 At Lincoln School there are 4 classes of fifth graders with 30 students in each class. Altogether, how many students are in the 4 classes?
Solution This story is about equal groups. We are given the number of groups (4 classes) and the number in each group (30 students).
We write an equation.
Number of groups ¥ number in each group = total 4 ¥ 30 = T
We multiply to find the missing number.
4 ¥ 30 = 120
We check whether the answer is reasonable. There are many more students in four classes than in one class, so 120 is reasonable. There are 120 students in all 4 classes.
Example 2 The coach separated 48 players into 6 teams with the same number of players on each team. How many players were on each team?
Number in each group Number of groups Total
¥
Lesson 21 103 Solution This is an “equal groups” story. The groups are teams. We are given the number of groups (6 teams) and the total number of players (48 players). We are asked to find the number of players on each team. We write an equation.
We find the missing number, a factor, by dividing.
There were 8 players on each team. The answer is reasonable because 6 teams of 8 players is 48 players in all.
Example 3 Monifa raked up 28 bags of leaves. On each trip she could carry away 4 bags. How many trips did it take Monifa to carry away all the bags?
Solution The objects are bags, and the groups are trips. The missing number is the number of trips. We show two ways to write the equation.
4N = 28
The missing number is a factor, which we find by dividing.
28 ÷ 4 = 7
Monifa took 7 trips to carry away all 28 bags.
LESSON PRACTICE
Practice set For problems a–d, write an equation and find the answer.
a. On the shelf were 4 cartons of eggs. There were 12 eggs in each carton. How many eggs were in all four cartons?
b. Thirty desks are arranged in 6 equal rows. How many desks are in each row?
N players on each team ¥ 6 teams
48 players on all 6 teams
8 6 Ä48
4 bags in each trip
¥ N trips
28 bags in all the trips
104 Saxon Math 6/5
c. Twenty-one books are stacked in piles with 7 books in each pile. How many piles are there?
d. If 56 zebus were separated into 7 equal herds, then how many zebus would be in each herd?
e. Write an “equal groups” story problem for this equation.
Then answer the question in your story problem.
6 ¥ $0.75 = T
MIXED PRACTICE
Problem set For problems 1–3, write an equation and find the answer.
1. The coach separated the PE class into 8 teams with the same number of players on each team. If there are 56 students in the class, how many are on each team? Use a multiplication pattern.
2. Tony opened a bottle containing 32 ounces of milk and poured 8 ounces of milk into a bowl of cereal. How many ounces of milk remained in the bottle?
3. The set of drums costs eight hundred dollars. The band has earned four hundred eighty-seven dollars. How much more must the band earn in order to buy the drums?
4. Draw an oblique line.
5. Write two multiplication facts and two division facts for the fact family 6, 7, and 42.
6. 8 Ķ™ 7. 6N = 42 8. 9 Ä£§
9. 6N = 48 10. 56 ÷ 7 11.
12. Compare: 24 ÷ 4 À 30 ÷ 6
13. 14. 15.
16. 6 ¥ 8 ¥ 10 17. 7 ¥ 20 ¥ 4
(21)
(16)
(11)
(12)
(19)
(19) (18) (19)
(18) (20) (20)
70 10
(4, 20)
(17)
367
¥ 8 (17)
$ .5 04
¥ 7 (17)
837
¥ 9
(18) (18)
Lesson 21 105 18. $40 – $29.34 19. R – 4568 = 6318
20. 5003 – W = 876
21. 22. 23.
24. If a dozen items are divided into two equal groups, how many will be in each group?
25. What are the next three terms in this counting sequence?
..., 50, 60, 70, 80, 90, _____, _____, _____, ...
26. Use words to show how this problem is read:
27. What number is the dividend in this equation?
60 ÷ 10 = 6
28. Below is a story problem about equal groups. After you find the answer to the question, use it to rewrite the last sentence as a statement instead of a question.
The books arrived in 5 boxes. There were 12 books in each box. How many books were in all 5 boxes?
29. The fraction A is equivalent to what percent?
(13) (14)
(14)
(10)
268 687
+ M (13)
$ .
$ . 9 65 2 43 + $1.45
(6) 382
+ 182 96
(21)
(1)
(20)
10 2
(20)
(21)
(Inv. 2)