Multiplication Estimation

Multiplication Estimation

Poll

How did you feel about yesterday's math lesson?

• Amazing! I could teach that lesson to another scholar!

• Great! I felt comfortable doing the math by myself.

• Okay. I still have some questions and am getting some questions wrong.

• Not good. I didn't understand it at all.

Multiple Choice

90 x 10

• 9,000

• 900

• 90

Multiple Choice

700 x 3,000

• 21,000

• 210,000

• 2,100,000

Multiple Choice

500 x 400

• 200,000

• 20,000

• 2,000

What is estimation?

Why is estimation useful?

How many scholars are in our class?

• 32 scholars

• But are there exactly 32 scholars in every class at UES?

• No. There are 11 classes, but I’m not sure exactly how many scholars are in each class. What could I do to find a number that is close to the actual number of scholars in our school?

• ESTIMATE!

 $32\ \times\ 11\ \approx$  

• Round 32 to the nearest ten.

•  $32\ \approx\ 30$  

• Round 11 to the nearest ten.

•  $11\ \approx\ 10$  

• So  $32\ \times\ 11\ \approx\ 30\ \times\ 10\ \approx$  

• 300! So there about 300 scholars at UES.

How to estimate multi-digit products:

• Round both factors to the largest place value. Ex: 674 x 809 $\approx$  700 x 800

• Multiply the leading digits. 7 x 8 = 56

• Multiply the powers of ten. 100 x 100 = 10.000

• Multiply the two answers together. 56 x 10,000 = 560,000

•  $674\times809\approx700\times800\approx\left(7\times8\right)\times\left(100\times100\right)\approx56\times10,000\approx560,000$  

Multiple Choice

 $567\times53\ \approx$  ___ x ___
First, round 567 to the nearest hundred. 
 $567\ \approx$  

• 500

• 600

Multiple Choice

 $567\times53\ \approx$  600 x ___
Next, round 53 to the nearest ten. 
 $53\ \approx$  

• 50

• 60

Multiple Choice

 $567\times53\ \approx$  600 x 50
Now we solve just like we did yesterday!

• 3,000

• 30,000

• 300,000

Again, $567\times53\approx600\times50$  

• 6 x 5 = 30

• hundred x ten = thousand

• 30 thousand = 30,000

Multiple Choice

Let's try another! Round each factor to the leading digit.

 $2,319\times8,590\approx$  

• 2,000 x 8,000 

• 3,000 x 8,000

• 2,000 x 9,000

• 3,000 x 9,000

Multiple Choice

Ok, now solve!

 $2,319\times8,590\approx\ 2,000\times9,000\approx$  

• 18,000

• 180,000

• 1,800,000

• 18,000,000

Multiple Choice

Go all the way! $789\times64\approx$  

• 42,000

• 420,000

• 48,000

• 480,000

Multiple Choice

ANOTHER ONE! $509\times7,721\approx$  

• 4,000,000

• 400,000

• 3,500,000

• 350,000

Multiple Choice

JUST ONE MORE! YOU'VE GOT THIS!  $8,899\times5,566\approx$  

• 4,500,000

• 45,000,000

• 5,400,000

• 54,000,000