add-and-subtract-decimals-mentally-with-up-to-3-decimal-digits

Welcome to Clip from Spiral logo

Interactive video lesson plan for: Add and subtract decimals mentally (with up to 3 decimal digits)

Activity overview:

This lesson focuses on using MENTAL MATH with decimals. First, we consider the sum 0.04 + 0.05, which many students mistakenly think equals 0.9 or 0.09. I show with number line jumps how it goes -- we "land" at 0.45.

You can also easily see it if you make both numbers have the same amount of decimals. Write 0.4 as 0.40, and the problem becomes 0.40 + 0.05, or 40 hundredths plus 5 hundredths, which clearly is 0.45.

We solve other addition and subtraction problems using the same tactic or "trick" - adding decimal zeros until all numbers have the same number of decimal digits. After that the problems become so much easier, and we can solve many with just mental math!

In the end, we also solve two problems by writing the decimals one under the other (add/subtract in columns), carefully aligning the decimal points and the different places.

This lesson is meant for 5th grade onward. I hope it is of help!

Tagged under: 5th grade,math,mental math,trick,decimal zeros,decimal addition,decimal subtraction,decimal digits,hundredths,add,subtract

Clip makes it super easy to turn any public video into a formative assessment activity in your classroom.

Add multiple choice quizzes, questions and browse hundreds of approved, video lesson ideas for Clip

Make YouTube one of your teaching aids - Works perfectly with lesson micro-teaching plans

Play this activity

1. Students enter a simple code

2. You play the video

3. The students comment

4. You review and reflect

* Whiteboard required for teacher-paced activities

Share on:

Share Add and subtract decimals mentally (with up to 3 decimal digits) on Google+ Share Add and subtract decimals mentally (with up to 3 decimal digits) on Twitter Share Add and subtract decimals mentally (with up to 3 decimal digits) on Facebook Pin Add and subtract decimals mentally (with up to 3 decimal digits) Email Add and subtract decimals mentally (with up to 3 decimal digits)

Ready to see what else Spiral logo can do?

With four apps, each designed around existing classroom activities, Spiral gives you the power to do formative assessment with anything you teach.

Quickfire

Carry out a quickfire formative assessment to see what the whole class is thinking

Discuss

Create interactive presentations to spark creativity in class

Team Up

Student teams can create and share collaborative presentations from linked devices

Clip

Turn any public video into a live chat with questions and quizzes

1000s of teachers use Spiral to deliver awesome, engaging activities that capture students' understanding during lessons.

Now it's your turn Sign up

Spiral Reviews by Teachers and Digital Learning Coaches

Spiral
Review of Spiral by teacher: Kathryn Laster @kklaster

Tried out the canvas response option on @SpiralEducation & it's so awesome! Add text or drawings AND annotate an image! #R10tech

Spiral
Review of Spiral by teacher: Room 220 Math Stars @3rdgradeBCE

Using @SpiralEducation in class for math review. Student approved! Thumbs up! Thanks.

Spiral
Review of Spiral by teacher: Miss Ord @ordmiss

Absolutely amazing collaboration from year 10 today. 100% engagement and constant smiles from all #lovetsla #spiral

Spiral
Review of Spiral by teacher: Adam J. Stryker @strykerstennis

Students show better Interpersonal Writing skills than Speaking via @SpiralEducation Great #data #langchat folks!

Spiral
Review of Spiral by teacher: Dr Ayla Göl @iladylayla

A good tool for supporting active #learning.

Spiral
Review of Spiral by teacher: Brett Erenberg @BrettErenberg

The Team Up app is unlike anything I have ever seen. You left NOTHING out! So impressed!

Get the Clip Chrome Extension & Create Video Lessons in Seconds

Add Clip to Chrome