Math
2.8
Choose a computation
method
Objective
For a variety of problems state the
computation method to be used and add
or subtract using that method.
Which Way?
I am going to read several addition and
subtraction problems.
Student 1: You will solve these problems
using the mental math strategy.
Student 2: You will solve these problems
in your spiral notebook using the paper
pencil method.
Student 3: You will solve these problems
using a calculator.
After each round rotate places.
Example: 38,509+20,321=
25,000+10,800=
3,000-1,999=
2,348+15,205+777=
9,525-6,305=
125+75+250=
Number Sense
Describe the exercises for
which mental math was the
quickest calculation method.
For which exercises was using
paper and pencil tedious?
When to use Mental Math?
We use mental math
when the problem is
easy to do in our
head.
When to use paper and pencil?
We use paper and pencil
when the problem is more
difficult but does not have
many regroupings.
When to use the calculator?
We use a calculator
when the math
problem has a lot of
regroupings.
Which Method Works Best
Decide what method
works best for each
problem.
1. 489- 235=
2. 520+70=
3.1,354-796=
Answers
1. Paper and Pencil
2. Mental Math
3. Calculator
Calculator Computation
Did you ever get a wrong answer using a
calculator? What did you do wrong?
Using your math spirals, write a short
paragraph listing different ways to get an
incorrect answer using a calculator. Then write
a list of tips for using the calculator properly.
Make sure you write complete sentences.
After you are finished writing we will share our
paragraphs.