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Welcome to this IRSC Adult Education Live Virtual Lesson

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Welcome to this IRSC Adult Education Live Virtual Lesson

Diana Lenartiene, Ed. S. moderator/instructor

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Estimating Sums,

Differences,

products and quotients

Vocabulary Review

- A Sum is the answer to an addition problem
- A Difference is the answer to a subtraction problem
- A Product is the answer to a multiplication problem
- A Quotient is the answer to a division problem
- Estimating means rounding the numbers in a problem to
- get an approximate or close answer

We will begin by working with estimating sums

and differences, then we will learn about how to

estimate products and quotients.

Let’s watch a video on estimating sums and differences now.

We need a little practice! Let’s try a few more

Problems to be sure we “get it!

Estimate the following sums and differences:

a 75 + 63

b 91 - 66

c 24 + 49 + 37

Answers

a 75 + 63 ≈ 80 + 60 ≈ 140

b 91 - 66 ≈ 90 – 70 ≈ 20

c 24 + 49 + 37 ≈ 20 + 50 ≈ 70

- As you can see, what we have actually done is to put two math skills together to complete each of the problems.
- First, we round all the numbers in the problem,
- Then, we add or subtract to find the approximate or estimated answer.

Now, let’s watch a video on

Estimating Products and

quotients

Let’s try these:

a 57 x 42

b 73 x 59

c 85 x 98

Answers

a 57 x 42 ≈ 60 x 40 ≈ 2,400

b 73 x 59 ≈ 70 x 60 ≈ 4,200

c 85 x 98 ≈ 90 x 100 ≈ 9,000

Let’s try these:

a 82 ÷ 4

b 103 ÷ 10

c 88 ÷ 3

Answers

a 82 ÷ 4 ≈ 80 ÷ 4 ≈ 20

b 103 ÷ 10 ≈ 100 ÷ 10 ≈ 10

c 88 ÷ 3 ≈ 90 ÷ 3 ≈ 30

As you can see, rounding, then completing the

operation, add, subtract, multiply or divide makes it

easy to figure out estimated sums, differences,

products and quotients.

Now what if we have to figure out how to set up the problem?

This will happen mostly with word problems, so let’s try some now.

Let’s try these:

a) In her bookcase, Lynda has 12 shelves. Estimate

the number of books in the bookcase if there are approximately

40 books on each shelf.

b) Miki reads 217 words in a minute. Estimate the number of words she can read in one hour.

c) A bricklayer lays 115 bricks each hour. If he

works a 37 hour week, approximately how

many bricks will he lay in one week?

d) Mike has a huge bag of M & M’s. There are 356 pieces

of candy in the bag. If there are 23 in the class counting

Mike and the teacher, approximately how many will

each person get if he shares them equally?

Answers

a) In her bookcase, Lynda has 12 shelves. Estimate the number of books in the bookcase if there are approximately 40 books on each shelf.

We need to set up a multiplication problem, because we have 12 shelves with approximately 40 books on each shelf,

so 40 x 10 will give us an estimate of 400 Books.

Answers

b) Miki reads 217 words in a minute. Estimate the number of words she can read in one hour.

There are 60 minutes in an hour. If Miki reads 217 words in a minute, we would have to multiply by 60 to get how many she would read in an hour.

So, 217 rounds to 210, and 60 is already rounded to the nearest ten.

210 x 60 ≈ 1,260

Answers

c) A bricklayer lays 115 bricks each hour. If he

works a 37 hour week, approximately how

many bricks will he lay in one week?

We know that we have to multiply again, so we will round

37 hours to 40 and the bricks to 110.

110 x 40 ≈ 4,400

Answers

d) Mike has a huge bag of M & M’s. There are 356 pieces of candy in the bag. If there are 23 in the class counting Mike and the teacher, approximately how many will each person get if he shares them equally?

We know we need to divide this time because we are going to share the M & M’s with

the class and the teacher. We can round the M & M’s to 360, and round the class to 20.

360 ÷ 20 ≈ 18

What we have learned:

- We can round numbers so that we can get estimated sums, differences,
- products and quotients.
- We can estimate word problems by choosing an operation, then rounding the numbers to find the estimated answer to the problem.
- We use estimation when we are not required to find the exact answer to a problem, or when an exact answer is not possible.

Now, you need to make a copy of this screen to send to your teacher for proof of

Attendance. This can be done in three easy steps:

If you still have questions, please contact me at:

Thank you for viewing this presentation.

Diana Lenartiene, IRSC ABE Instructor