## Mental Addition and Subtraction of 10s or 100s

#### Aligned To Common Core Standard:

**Grade 2 Base Ten** - 2.NBT.8

Tips for Mental Addition and Subtraction
Gathering all the praise by yourself for doing mental math is just awesome, isn't it? To be able to solve two and three-digit numbers within a few minutes without having to use a calculator not only boosts your confidence, but it also amplifies your comprehension too. Mental math is associated with number sense, which is the skill to manipulate numbers in your head in one or more ways to solve simple and complex problems. Reportedly, having number sense has an impact on the achieving grasp over algebra.
A few tricks to do mental math are:
1.The '9-trick.'- If you have to add 9 to any number, the trick is to add 10, get the answer, and then instantly minus 1 in your head. You have your final answer. Do the same for subtraction.
2. Learn +1 double - Memorizing sum of doubles is a great way to get a grasp over mental mathematics. By the sum of doubles, we mean; 7+7, 10+10, 30+30, etc. This way, you can quickly add one more to the answer if you get to solve a ‘double plus one more,' for a sum 7+8, add 7+7, then add one more to the answer.
3.Subtract by adding- This trick is based on the connection between addition and subtraction. To find out, find 8 − 6, think, "6 plus how much more makes 8?"

6 + ___ = 8.

This is going to be your answer for 8 – 6 too.
This collective of worksheets has students practice the mastery of mental math facts.

### Printable Worksheets And Lessons

- Step-by-step Lesson- I broke
out the numbers line to help us. We move between the addition and
subtraction of 10s.

- Guided Lesson
- The focus is on on the movement between tens place again here.

- Guided Lesson Explanation
- Sorry, I might have gone a bit overboard with explaining here.
I just wanted to make sure a students wouldn't need any outside
help.

- Practice Worksheet
- Ten problems that all use a numbers line to prompt the students.

- Matching Worksheet - Match the missing numbers line spot to the number that is missing.

#### Homework Sheets

Fill in the partially missing parts of the numbers line.

- Homework 1- Complete the number lines below.
- Homework 2
- Homework 3

#### Practice Worksheets

You will start with blank number lines; except for the start and finish.

- Practice 1- Find the final value of the following problem.
- Practice 2
- Practice 3