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Multiplying Whole Numbers and Decimals

Multiplying Whole Numbers and DecimalsLesson 2-2Things you need to knowDo not line up the decimal points!

Pretend all decimals are whole numbers until the very endOnly look at the decimals when trying to figure out where to put the decimal point in your answerStrategy #1405 59 = x 405x 59or 405x 50 405x 9+455 x 9 = 45Put the 5 in the answer and carry the 4 (its really 40) to the next place value (tens)4(9 x 0) + 4 = 4

Write down the 4.36(9 x 4) = 36

Since there are no other numbers to multiply, write down the 36.Zero is a place holder. Put a zero in your answer to hold its place.0255 x 5 = 25Put the 5 in the answer and carry the 2 (its really 20) to the next place value (tens)(5 x 0) + 2 = 2

Write down the 2.02(5 x 4) = 20

Since there are no other numbers to multiply, write down the 20.2Strategy #1405 59 = x 405x 59or 405x 50 405x 9+4543602502223,895The final answer is:Strategy #2The Lattice 405x 59There are 3 digits in this numberThere are 2 digits in this numberWe will start by making a 3 x 2 windowStrategy #2The Lattice 405x 593 digits2 digitsStrategy #2The Lattice 405x 5940559xPut diagonal lines in each of the windows.Strategy #2The Lattice 405x 5940559xMultiply one number from the top with one from the side. Put your answer in the box where they meet.4 x 5 = 2020Strategy #2The Lattice 405x 5940559x5 x 0 = 02000Strategy #2The Lattice 405x 5940559x5 x 5 = 25200025Strategy #2The Lattice 405x 5940559x4 x 9 = 3620002536Strategy #2The Lattice 405x 5940559x0 x 9 = 02000253600Strategy #2The Lattice 405x 5940559x5 x 9 = 45200025360045Strategy #2The Lattice 405x 5940559x200025360045Now we will add numbers diagonally from right to leftStrategy #2The Lattice 405x 5940559x2000253600455983223895What if I have a decimal point in my problem?Multiply your numbers using one of the steps just shown.When done, count all the numbers after a decimal point in your problem.Make sure your answer has exactly that number of digits in the decimal spaces.If my problem has decimals 4.05x 5.923,895 4.05x 5.9 405x 5923.895 .405x .059 .405x .059.023895I had to add a zero because there are six total decimals spots in my problem, but I only had 5 digits in my answer. Notice that the zero came between the decimal point and my old answer.Lets try one moreStrategy #2The Lattice 395x 84There are 3 digits in this numberThere are 2 digits in this numberWe will start by making a 3 x 2 windowStrategy #2The Lattice3 digits2 digits 395x 84Strategy #2The Lattice39584xPut diagonal lines in each of the windows. 395x 84Strategy #2The Lattice39584xMultiply one number from the top with one from the side. Put your answer in the box where they meet.8 x 3 = 2424 395x 84Strategy #2The Lattice39584x8 x 9 = 722472 395x 84Strategy #2The Lattice39584x8 x 5 = 40247240 395x 84Strategy #2The Lattice39584x4 x 3 = 1224724012 395x 84Strategy #2The Lattice39584x4 x 9 = 362472401236 395x 84Strategy #2The Lattice39584x4 x 5 = 20247240123620 395x 84Strategy #2The Lattice39584x247240123620Now we will add numbers diagonally from right to left 395x 84Strategy #2The Lattice39584x247240123620081333380 395x 84111What if I have a decimal point in my problem?Multiply your numbers using one of the steps just shown.When done, count all the numbers after a decimal point in your problem.Make sure your answer has exactly that number of digits in the decimal spaces.If my problem has decimals39.5x 8.433180 39.5 x 8.4331.80 .395x .084 .395x .084.033180I had to add a zero because there are six total decimals spots in my problem, but I only had 5 digits in my answer. Notice that the zero came between the decimal point and my old answer. 395x 84Lets Practice78.6 x 983798863637254566448212418831612271777263.8There is one digit after a decimal point.772638.392 x .0083009280000000000002472166311300.003136There are 6 digits after a decimal point.0031369358 x .32807.4115.6 x .004.4624.0018 x 7.0216