MULTIPLYING DECIMALS Lesson 3 4 Using Base Ten

MULTIPLYING DECIMALS Lesson 3. 4

Using Base Ten Blocks The flat represents 1, the rod represents 0. 1 and the small cube represents 0. 01 By using Base Ten Blocks to make a rectangle, you can switch to addition instead of multiplication for decimals.

Modeling A rectangular park measures 1. 7 km by 2. 5 km. Step 1: Build a rectangle with length of 2. 5 and width 1. 7 Width (1. 7 km) Length (2. 5 km) When the rectangle is finished, count the blocks in the rectangle.

There should be 2 flats: 2 x 1 = 2 There should be 19 rods: 19 x 0. 1 = 1. 9 There should be 35 cubes: 35 x 0. 01 =. 35 The total area will be: 2 + 1. 9 +. 35 = _____

But How Do I Multiply? ? 1. 7 x 2. 5 Pretend there are no decimals. 17 x 25 Multiply as normal. Then add the decimal after.

But Where Do I Put The Decimal? 1. 7 x 2. 5 4. 25 Ask yourself, “How many numbers are after the decimal? ” = Ask 1 yourself, “How many numbers are after the decimal? =1 There are 2 numbers total after the decimal point. Start at the end of the number, then, move two numbers to the left. Where you stop the decimal goes.

How Do I Multiply 2 Two Digit Numbers? A brief reminder. . . 13 x 12 26 190 216 1) Multiply 3 x 2 first. Put the answer below the 2. (6) 2) Then, multiply 2 x 1. Put the answer beside the 2 and under then 1. (2) 3) Then, put a zero under the 2. (0) 4) Then multiply 1 x 9. Put the answer beside the zero and under the 1. (9) 5) Then, multiply 1 x 1. Put this answer beside the 9. 6) Add the two numbers together to get your answer.

Try these with long multiplication. a) 14 x 21 b) 17 x 12 c) 15 x 20

Word Problems At the Farmers Market, 1 kg of grapes costs $2. 95. How much would 1. 8 kg of grapes cost? 1 kg of grapes costs $2. 95. So, 1. 8 kg would cost 2. 95 x 1. 8 Create a rectangle model (Base Ten)

2. 95 x 1. 8 2. 95 2. 0 x 1. 0 0. 95 x 1. 0 1. 8 2. 0 x 0. 8 0. 95 x 0. 8 (2. 0 x 1. 0) + (0. 95 x 1. 0) + (2. 0 x 0. 8) + (0. 95 x 0. 8) (2 x 1) + (0. 95) + (2 x 0. 8) +(0. 95 x 0. 8) 2 + 0. 95 + 1. 6 + 0. 76 = 5. 31 Therefore, 1. 8 kg of grapes would cost $5. 31.

A kg of apples costs $1. 90. How much would 2. 1 kg of apples cost? Draw the rectangle model and solve.

An area rug is rectangular. Its dimensions are 3. 4 m by 2. 7 m. Solve using multiplication.

Estimation To estimate using multiplication, multiply the two whole numbers together. (First round up or down to the nearest whole number) 5. 3 x 2. 1 = 5 x 2 = 10 A good estimation is 10. Multiply to verify your estimation.

Use estimation, then solve using multiplication. Remember to round up or down to the nearest whole number) a) 2. 6 x 1. 3 b) 7. 2 x 4. 8 c) 3. 9 x 3. 2

Homework Workbook 3. 4 Textbook Page 102 – 103 # 4, 5, 9, 10 and Reflect