Topic 2, Lesson 2 Mental Math: Estimate Sums and Differences

Topic 2, Lesson 2 Mental Math: Estimate Sums and Differences

Multiple Choice

What is a sum?

• The answer to any math problem.

• The answer to an addition problem.

• The answer to a subtraction problem.

Multiple Choice

What is a difference?

• The answer to any math problem.

• The answer to an addition problem.

• The answer to a subtraction problem.

The Essential Understanding

of this lesson is:

There is more than one way to estimate a sum or difference. Estimation gives a way to replace numbers with other numbers that are close and easier to compute mentally.

Reminder

Mental math is being able to mental math calculations in your head. But it is okay to use paper and pencil and record your thought process to get to the answer!

One strategy we can use to add and subtract in our head is to use rounding.

We can ESTIMATE the sums and differences of numbers.

Multiple Choice

True or False: You can estimate to any place value.

• True, but you should be

  precise in your choice.

• False, you have to

  estimate to the hundreds place.

Let's estimate the sum of an addition problem. We will round to the hundred place.

33,498 + 28,609

Poll

What is 33,500 + 28,600?

• 62,000

• 62,100

• 62,200

This time we will round to the thousand place.

33,498 + 28,609

Poll

What is 33,000 + 29,000?

• 62,000

• 62,100

• 62,200

This time we will round to the ten thousand place.

33,498 + 28,609

Poll

What is 30,000 + 30,000?

• 62,000

• 62,100

• 62,200

• 60,000

Each answer was a little different.

That answer is closer to the actual number based on what place you round to.

This same thing applies to subtraction.

Notice the differences when we change the place value to we round to.

Open Ended

What do you notice about the sum or difference as you round further away from the ones and tens?

Multiple Choice

Estimate the sum, rounding each number to the one thousand place.

• 5,000 + 2,000 = 7,000

• 5,000 + 2,600 = 7,600

• 5,000 + 3,000 = 8,000

Multiple Select

To the nearest ten thousand, Calvin estimates the difference of a subtraction problem at 220,000. Select all that could have been Calvin’s original problem.

• 232,684 - 14,652

• 238,041 - 19,558

• 271,982 - 64,780

• 298,155 - 75,437

• 242,698 - 18,765

Next Steps:

Go to Schoolwork to Open EdPuzzle.

Don't forget to Mark Done when you finish EdPuzzle.

Then Open Keynote Practice Buddy.

Don't forget to Submit when you finish.