Dividing Decimals Dash!
Students will be able to divide decimals by whole numbers.
- Tell students that today they will be learning how to divide decimals by whole numbers.
- Ask students to think of a time when they would need to divide a decimal by a whole number. Take several examples. If students are having trouble thinking of an example, remind them that money is represented as a decimal.
- Give students an example. Example: You and your two friends ran a lemonade stand. You made $63.12. How much money would each person get?
- Write out this word problem as an expression and use the standard algorithm for division. Show students that the divisor, or the number to be divided by, would be three and the dividend, or the number being divided, would be $63.12.
Explicit Instruction/Teacher modeling(15 minutes)
- Go back to the problem written on the board (63.12 ÷ 3).
- Explain that the first step is to write a decimal point where the quotient, or the answer to a division problem, will be, directly above the decimal point in the dividend.
- Tell students that the rest of the problem is just like a long division problem with whole numbers. Remind students to use the following acronym to remind them how to perform each step in long division: Dad, Mom, Brother, Sister (Divide, Multiply, Bring Down, Subtract).
- Work out the problem for students to see. (The answer is $21.04.)
- Give two more examples for students to see and have students help you walk through each step.
Guided Practice(15 minutes)
- Explain that students will be doing a relay race to solve decimal division problems.
- Students will be divided into groups of four. Each student will get a different task: divide, multiply, bring down, or subtract. You can assign students groups and tasks, or allow them to choose their own groups and tasks.
- Explain that you will give the class a division decimal problem. The "divide" person will begin by writing the problem on the whiteboard or chart paper. The rest of the group will line up behind them in order of their tasks.
- When you say "go," the person dividing will complete the first step of the problem. They will then hand the marker to the next person, who will complete her task. This will continue until the problem is solved. The entire group will sit down when the problem is complete to show the teacher they are finished.
- Tell students that they are allowed to help their teammates, but they cannot leave the line or yell. Remind students that they don't want to talk too loudly, or another group may hear them!
- Remind students that in order to win, they must not only finish first, but also have the correct answer.
- Start the game. (Possible problems: 77.21 ÷ 3; 90.4 ÷ 2; 5.15 ÷ 5.)
Independent working time(15 minutes)
- Hand out lined paper to each student.
- Give students the following additional problems to work on independently: 55.20 ÷ 5; 9.081 ÷ 9, 4.97 ÷ 7.
- Review each problem with students. Choose students to tell the class the order they used to solve the division problem.
- Some students may struggle with long division if they have trouble with factors and multiplication facts. These students can use a multiplication chart to help them as they work through the problems. These students could also have an example problem worked out for them to refer to as they complete problems.
- Challenge students to write their own word problems that require dividing decimals by whole numbers. Students can trade their problems with a classmates and solve them!
- Tell students to solve the following problem on their lined sheet of paper: $25.60 ÷ 4 and tell them to solve the problem and list the steps they used to solve it (e.g., Divide, Multiply, Bring Down, Subtract).
- Use the three problems from independent work time and this assessment to determine your students' understanding of dividing decimals by whole numbers.
- Understand that some common errors include mixing up or forgetting steps for long division, placing the decimal point in the wrong place, or simple multiplication errors. If several students have made the same mistake, address this by reteaching the skill in a small group.
Review and closing(5 minutes)
- Ask students what the most challenging part of the relay race was.
- Remind students that although the relay race was a fun challenge, it is important to think carefully and take your time when completing math problems to ensure they are done correctly!