EnVision Math

Topic 5:

Lesson 5-3 & 5-4 Combined

Multiplying by 1-Digit Numbers:

Using Rounding to Estimate

2010-11

Sarah earns $48 a week babysitting. She has saved all her money for the past 6 weeks. About how much money has she earned?

About

How can I

estimate products

?

645 + 253 =600 300

900

72,694 - 17,789 =70,000 20,000

50,000

52 x 9 =50 x 9

450

6 x 34 =6 x 30

180

314 x 7 =300 x 7

2,100

3 x 538 =5003 x

1,500

39 x 5 =40 x 5

200

9 x 602 =9 x 600

5,400

3 x 86 =3 x 90

270

486 x 7 =500 x 7

3,500

77 x 8 =80 x 8

640

2 x 863 =2 x 900

1,800

3,752 x 9 = 4,000 x 9

36,000

7 x 5,835 =7 x 6,000

42,000

6,987 x 8 = 7,000 x 8

56,000

4 x 5,125 = 4 x 5,000

20,000

Sarah earns $48 a week babysitting. She has saved all her money for the past 6 weeks. About how much money has she earned?

50 x 6 =$300

There are 78 fifth grade students at Lincoln Elementary. Each fifth grader brought in 7 cans for the recycling drive. About how many cans did the fifth graders collect?

80 x 7 = 560 cans

Ursula has an album that she keeps pressed flowers in. The album has 34 pages, and each page has 7 pressed flowers. Which of the following shows a reasonable estimate for how many pressed flowers Ursula has?

A. 40 x 7 = 280 pressed flowers

B. 30 x 7 = 210 presses flowers

C. 40 x 10 = 400 pressed flowers

D. 30 x 10 = 300 pressed flowers

Isabelle has 9 ant farms. Each ant farm has 99 ants. Which of the following is a reasonable estimate of how many ants Isabelle has?

A. 9 x 90 = 810 ants

B. 10 x 100 = 1,000 ants

C. 9 x 80 = 720 ants

D. 9 x 100 = 900 ants

How can I use estimation to check if my answer is

reasonable?

There are 5 animals on a farm. Each animal eats 105 pounds of food per week. How much food does the farmer have to buy each week?

105 x 5 = 525 pounds of food100 x 5 = 500

Kenny has 7 pouches. Each pouch has 21 marbles. How many marbles does Kenny have?

7 x 21 = 147 pouches

7 x 20 = 140

marbles

A fish store has 3 empty tanks. After a delivery, they put 29 fish in each tank. How many fish were in the delivery?

3 x 29 = 627 fish

3 x 30 = 90

87