Lesson on Estimating Products

Topic 3, Lesson 2: Mental Math: Round to Estimate Products

Rounding

Rounding is a process that determines which multiple of 10, 100, 1,000, and so on a number is closest to.

Rounding Review

In order to round 3,524 to the nearest thousand:

1) Look at the digit to the right of the thousands place.

2) Add 1 to the digit in the rounding place. Then write 3 zeros.

Multiple Choice

3,524 rounded to the nearest thousand is:

• 3,500

• 3,000

• 4,000

• 4,024

Rounding Rules

5 or more ☝️ (+1)

4 or less 💤 (stay the same)

Let's use rounding to estimate 6 × 789.

Multiple Choice

Round 789 to the nearest hundred.

• 700

• 780

• 790

• 800

Multiple Choice

Now multiply 6 x 800.

• 4,600

• 4,800

• 4,880

• 5,000

You can also use rounding to check if a product is reasonable.

Multiple Choice

Let's Check if 5 × 3,011 = 15,055 is reasonable.

Start with: What is 3,011 rounded to the nearest thousand?

• 3,000

• 3,011

• 4,000

Multiple Choice

Now multiply 5 x 3,000. What is the product?

• 1,500

• 15,000

• 150,00

• 15,055

Story Problem

Jenny worked 7 weeks. She made $417 per week. About how much money did she make after 7 weeks?

Multiple Choice

Estimate the product of 7×417 by using rounding. What is the product?

• She made about $2,919.

• She made about $2,900.

• She made about $2,819.

• She made about $2,800.