MR 2.5
Indicate the relative advantages of exact and approximate
solutions to problems and give answers to a specified degree of
accuracy.
UNDERLYING SKILLS AND CONCEPTS:
read word problems
Decide When to Estimate
a
K
ey Ide
When you solve word problems, remember
to use the four-step problem-solving plan.
Read carefully. Sometimes you can estimate.
E x am p l E
There are 12 people at Tomiwa’s birthday party.
He has 2 packages of water balloons
with 25 balloons in each package.
Can each person have at least 3 balloons?
Step 1: What question do you need to answer?
Are there enough balloons for each friend to have three?
C – © CSL Associates, Inc. All rights reserved.
Step 2: What information do you have?
There are 12 people.
There are 2 packages of balloons.
Each package has 25 balloons.
Step 3: How will you solve the problem?
You do not need to find an exact answer.
So, you can estimate.
First find the total number of balloons.
2 packages of 25 balloons 50 balloons
To estimate, find a compatible division fact
for 50 and 12.
For example, you can round 12 to 10.
Then divide to estimate. 50 ÷ 10 5
Yes, each person can have at least 3 water balloons.
Step 4: Check.
Use the inverse operation.
Multiply the number of balloons by the number of people.
3 12 36. There are enough.
page 138
Chapter 12 – Lesson 3
Name
P RAC T I C E
Decide whether to estimate or to find an exact answer. Then solve.
Explain your solution strategy.
1. Mai-ling has $1.00 to spend at the snack stand.
SNACK PRICES
Does she have enough to buy 3 items?
No. Estimate. The least expensive item is
about 40¢. 3 40 120, which is more
than a dollar.
2. If Mai-ling’s sister gives her $1 more, how much
change will she have if she buys a pretzel, popcorn,
and a popsicle? $0.55 left
pretzels
50¢
peanuts
45¢
popcorn
60¢
popsicle
35¢
Exact answer. Add the cost of each item.
$0.50 $0.60 $0.35 $1.45 & $2.00 $1.45 $0.55
3. A video tape has 6 hours of
recording time. Can you record
C – © CSL Associates, Inc. All rights reserved.
1
a 21
hour movie and a 1 hour
2
2
4. Does Rebecca have enough with
11
yards of gold trim to trim
4
ball game? Yes. Estimate.
the perimeter of a hexagonal
ornament that has 3-inch sides?
The movie lasts about
3 hours. The ball game lasts
about 2 hours. 3 2 5
Yes, a 6 hour-tape is enough.
Yes. Mixed methods. The
ornament has a perimeter of
6 3, or 18 inches. A yard is
36 inches. She has enough.
Math
Reasoning
Estimation
MR 2.5
5. The attendance at the concert was 1,347 on Thursday, 1,568 on Friday,
and 1,624 on Saturday. Write a problem that needs an estimate. Write
a problem that needs an exact answer.
Possible answers: About how many people attended the
concert? (estimate 5,000). How many more people came on
Saturday than on Thursday? (1,624 1,347 277)
Chapter 12 – Lesson 3
page 139
MCX94.HW.CL.G3.FM&Lesson.v211
8/3/04
13:56
Page 94
Name
P RAC T I C E
…at home!
Decide whether to estimate or to find an exact answer. Then solve.
Explain your solution strategy.
1. Emilia has $1.00 to spend at the snack stand. Does
SNACK PRICES
she have enough to buy 2 items?
Yes. Estimate. The least expensive item is
about 40¢. 2 40 80, which is less
than a dollar.
2. If Emilia’s sister gives her $1 more, how much
change will she have if she buys peanuts, popcorn,
and a popsicle? $0.60 left
pretzels
50¢
peanuts
45¢
popcorn
60¢
popsicle
35¢
3. A video tape has 6 hours of
4. Does Rebecca have enough with
recording time. Can you record
11
yards of gold trim to trim
4
1
1
two 2 hour movie and a 1 hour
2
2
the perimeter of a square
ornament that has 4-inch sides?
ball game? No. Estimate.
The movies last about
3 hours each. 2 36.
The ball game lasts about
2 hours. 6 2 8
No, a 6-hour tape is not enough.
Math
Reasoning
Yes. Estimate. The
ornament has a perimeter of
4 4, or 16 inches. A yard is
36 inches. She has enough.
Estimation
MR 2.5
5. The attendance at the concert was 1,237 on Thursday, 1,689 on Friday,
and 1,726 on Saturday. Write a problem that needs an estimate. Write
a problem that needs an exact answer.
Possible answers: About how many people attended the
concert? (estimate 5,000). How many more people came on
Saturday than on Thursday? (1,726 1,237 489)
page 94
Home Resource and Homework
Chapter 12 Lesson 3
C – © CSL Associates, Inc. All rights reserved.
Exact answer. Add the cost of each item.
$0.45 $0.60 $0.35 $1.40 & $2.00 $1.40 $0.60
MCX94TEG3Ch01_32.v8.9.3 2/21/01 14:46 Page 257
Name
P RAC T I C E
Decide whether to estimate or to find an exact answer. Then solve.
Explain your solution strategy.
1. Mai-ling has $1.00 to spend at the snack stand.
SNACK PRICES
Does she have enough to buy 3 items?
No. Estimate. The least expensive item is
about 40¢. 3 40 120, which is more
than a dollar.
2. If Mai-ling’s sister gives her $1 more, how much
change will she have if she buys a pretzel, popcorn,
and a popsicle? $0.55 left
pretzels
50¢
peanuts
45¢
popcorn
60¢
popsicle
35¢
Exact answer. Add the cost of each item.
$0.50 $0.60 $0.35 $1.45 & $2.00 $1.45 $0.55
3. A video tape has 6 hours of
recording time. Can you record
C – © CSL Associates, Inc. All rights reserved.
1
a 21
hour movie and a 1 hour
2
2
4. Does Rebecca have enough with
11
yards of gold trim to trim
4
ball game? Yes. Estimate.
the perimeter of a hexagonal
ornament that has 3-inch sides?
The movie lasts about
3 hours. The ball game lasts
about 2 hours. 3 2 5
Yes, a 6 hour-tape is enough.
Yes. Mixed methods. The
ornament has a perimeter of
6 3, or 18 inches. A yard is
36 inches. She has enough.
Math
Reasoning
Estimation
MR 2.5
5. The attendance at the concert was 1,347 on Thursday, 1,568 on Friday,
and 1,624 on Saturday. Write a problem that needs an estimate. Write
a problem that needs an exact answer.
Possible answers: About how many people attended the
concert? (estimate 5,000). How many more people came on
Saturday than on Thursday? (1,624 1,347 277)
Chapter 12 – Lesson 3
Student Book Page
page 139
Name
P RAC T I C E
…at home!
Decide whether to estimate or to find an exact answer. Then solve.
Explain your solution strategy.
1. Emilia has $1.00 to spend at the snack stand. Does
SNACK PRICES
she have enough to buy 2 items?
Yes. Estimate. The least expensive item is
about 40¢. 2 40 80, which is less
than a dollar.
2. If Emilia’s sister gives her $1 more, how much
change will she have if she buys peanuts, popcorn,
and a popsicle? $0.60 left
pretzels
50¢
peanuts
45¢
popcorn
60¢
popsicle
35¢
3. A video tape has 6 hours of
4. Does Rebecca have enough with
recording time. Can you record
11
yards of gold trim to trim
4
1
1
two 2 hour movie and a 1 hour
2
2
the perimeter of a square
ornament that has 4-inch sides?
ball game? No. Estimate.
The movies last about
3 hours each. 2 36.
The ball game lasts about
2 hours. 6 2 8
No, a 6-hour tape is not enough.
Math
Reasoning
Yes. Estimate. The
ornament has a perimeter of
4 4, or 16 inches. A yard is
36 inches. She has enough.
Estimation
MR 2.5
5. The attendance at the concert was 1,237 on Thursday, 1,689 on Friday,
and 1,726 on Saturday. Write a problem that needs an estimate. Write
a problem that needs an exact answer.
Possible answers: About how many people attended the
concert? (estimate 5,000). How many more people came on
Saturday than on Thursday? (1,726 1,237 489)
page 94
Home Resource and Homework
Chapter 12 Lesson 3
C – © CSL Associates, Inc. All rights reserved.
Exact answer. Add the cost of each item.
$0.45 $0.60 $0.35 $1.40 & $2.00 $1.40 $0.60