MathGrade 4 Mrs. Ennis Multiplying Two 2 Digit Numbers Lesson Twenty-Eight
23 + 456 + P + 803 = 1292 Find the difference of these two numbers: 3456 and 8496 7 X Y = 42 M x 3 = 81 40 ÷ F = 8 1 day = ________ hours
7. Three pennies + five quarters = 8. What would you subtract from 1492 to change the 4 to a zero? 9. Mr. White read 3 chapters on Monday, 5 chapters on Tuesday, 7 chapters on Wednesday. If this pattern continues, on what day will he read 21 chapters?
10. Mario wrote a story about dinosaurs. The story had 325 words. When he edited the story, he deleted 36 words and added 82 new words. How many words are in the story now?
Multiplying Two 2 Digit Numbers
Let’s Review Factors- Numbers multiplied together Product- The answer in a multiplication equation
Two Digit Multiplication We can break this down into two problems: 26 26 26 x 2 x x 12 10 26 x 2 26 x 10
Two Digit Multiplication 26 x 12 26 26 x 2 x 10 52 260
Two Digit Multiplication 26 26 26 260 x x x 12 2 10 + 52 3 1 2
Two Digit Multiplication We can break this down into two problems: 53 53 53 x 4 x x 24 20 53 x 4 53 x 20
Two Digit Multiplication 53 x 24 53 53 x 4 x 20 212 1260
Two Digit Multiplication 53 53 53 1260 x x x 4 24 20 + 212 1 4 7 2
Now, let’s try the ALGORITHM!
Two Digit Multiplication The first step is to make sure the place values are lined up. 26 x 12 Tens Ones
Two Digit Multiplication Begin by multiplying the bottom factor’s ones place with the top factor’s ones place. Because there is still the tens place to multiply, you must carry the 1. Think, 2 x 6 equals 12. 1 26 x 12 2
Two Digit Multiplication Next, multiply the ones of the bottom factor and the tens of the top factor. Remember to add your carry of 1. Think, 2x2=4,+1=5 1 26 x 12 5 2
Two Digit Multiplication Mark out or erase your carry from before. Next, we are going to the tens place so we need to use a 0 for a place holder. Put a 0 under the 2 in the products line. x 1 26 x 12 5 2 0
Two Digit Multiplication Next, begin to multiply the 1in the tens place with the ones place of top line factor. Think 1x6=6. 26 x 12 5 2 6 0
Two Digit Multiplication 26 Next, multiply the 1in the tens place with the tens place of top line factor. Think 1x2=2. x 12 5 2 2 6 0
Two Digit Multiplication 26 Finally, add the two product lines to find the final product. x 12 5 2 1 + 2 6 0 3 1 2
Two Digit Multiplication The first step is to make sure the place values are lined up. 34 x 25 Tens Ones
Two Digit Multiplication Begin by multiplying the bottom factor’s ones place with the top factor’s ones place. Because there is still the tens place to multiply, you must carry the 2. Think, 5 x 4 equals 20. 2 34 x 25 0
Two Digit Multiplication Next, multiply the ones of the bottom factor and the tens of the top factor. Remember to add your carry of 2. Think, 5x3=15,+2=17 2 34 x 25 17 0
Two Digit Multiplication Mark out or erase your carry from before. Next, we are going to the tens place so we need to use a 0 for a place holder. Put a 0 under the 0 in the products line. x 2 34 x 25 17 0 0
Two Digit Multiplication Next, begin to multiply the 2 in the tens place with the ones place of top line factor. Think 2x4=8. 34 x 25 17 0 8 0
Two Digit Multiplication 34 Next, multiply the 2 in the tens place with the tens place of top line factor. Think 2x3=6. x 25 17 0 6 8 0
Two Digit Multiplication 34 Finally, add the two product lines to find the final product. x 25 17 0 1 + 6 8 0 8 5 0
Let’s Practice!
34x 19 • 656 • 646 • 677 • No of these
Two Digit Multiplication 3 34 x 19 3 0 6 3 4 + 0 6 4 6
54x 23 • 1,242 • 1,244 • 1,342 • 1,142
Two Digit Multiplication 1 54 x 23 1 6 2 10 8 + 0 1 2 4 2
41x 18 • 748 • 778 • 738 • 728
Two Digit Multiplication 41 x 18 3 2 8 4 1 + 0 7 3 8
68x 35 • 2,370 • 2,345 • 3,270 • 2,380
Two Digit Multiplication 2 4 68 x 35 3 4 0 20 4 + 0 2 3 8 0
76x 52 • 3,952 • 4,952 • 3,852 • 3,552
Two Digit Multiplication 3 1 76 x 52 1 5 2 + 38 0 0 3 9 5 2
94x 76 • 7,044 • 7,144 • 6,044 • 6,244
Two Digit Multiplication 2 2 94 x 76 5 6 4 65 8 + 0 7 1 4 4
Online Practice http://www.mrnussbaum.com/draggable/multiplication.html http://www.mathplayground.com/multiplication05.html
Math Fun: Some fourth grade students are standing in a circle. They are evenly spaced and numbered in order. The 3rd student is directly opposite the 7th. How many students are in the circle?
Answer: There are 8 students in the circle.
Resources: http://mathlearnnc.sharpschool.com/UserFiles/Servers/Server_4507209/File/Instructional%20Resources/G4WW1-4.pdf • http://www.wcboe.org/teachers/mguy/powerpoints/ • http://www.mathplayground.com/multiplication05.html • http://www.mrnussbaum.com/draggable/multiplication.html
