1st Class Mathematics Addition and Subtraction Addition and Subtraction

Category : 1st Class

LEARNING OBJECTIVES

• understand the concept of addition and subtraction
• add 1 digit and 2 digit numbers (up to 20)
• subtract 1 digit and 2 digit numbers (up to 20)
• add and subtract numbers without using paper and pencil.

QUICK CONCEPT REVIEW

Suppose, you have 3 chocolates and you friend has given you 2 more chocolates. Now, how many chocolates in detail.

Putting things together is called addition.

When we add, we combine two or more numbers to make a new number. Which is known as ‘sum’. ‘+’ is the sign of addition. This sign is called plus sign.

Let us understand with the help of an example:

Tiya makes 5 paper boats and floats them in the pond. John makes 3 paper boats and floats them in the pond.

How many paper boats are there in the pond?

This problem can be solved by adding the number of boats made by Tiya and John.

Amazing Facts

If you add up the number 1-100 consecutively (1+2+3+4+5…) the total is 5050.

The opposite side of a die always add up to seven (7).

Real Life Examples

Addition helps to get the total amount of money spend in buying things from grocery shop.

Subtraction helps in calculating the pocket money left in our piggy bank.

1. Addition by counting,

We can add the total numbers of boats present in the pond by counting all the boats one by one.

2. Addition using number line

We have learnt about number line in previous chapter. Lets discuss how number line helps in adding two numbers.

For example.

Minki the cat, wants to add 4 and 2. Minki starts from 4 and reaches 2 steps ahead by jumping one step at a time

Minki reaches at number 6, i.e. 4 + 2 = 6.

3. Addition of zero and one to a number

On adding zero to a number, we get the number itself.

7 + 0 = 7

On adding 1 to a number, we get the number that comes just after it.

7 + 1 = 8

4. Addition by forward counting:

To add 2 to 7, count 2 numbers after 7.

To add 7 to 12, count 7 numbers after 12.

Historical Preview

The plus (+) and (-) signs are mathematical symbols used to represents addition and subtraction. These words are originated from latin term which means more and less respectively

To add 5 to 15, count 5 numbers after 15.

5. Adding by regrouping or vertical addition:

For adding numbers by regrouping, regroup the numbers into two columns of place value, tens and ones. Add each column, starting with the ones place and move towards left. For example for adding number 10 and 2.

SUBTRACTION

Suppose there are 6 apples in a fruit basket. 2 apples are eaten by Gannu. How many apples will be left? How will you calculate? This problem can be solved by subtraction.

Subtraction means taking away something from a group. The result of subtraction is known as 'difference'.

The sign used for subtraction is minus (-)

METHODS OF SUBTRACTION

1. Vertical Subtraction:

Just like addition, we can do subtraction vertically. Suppose Ram has 8 pencils, out of which he has given 5 pencils to Shyam. How many pencils are left with him now?

2. Subtraction Using The Number Line:

Roni Rabbit wants to subtract 3 from 18. Roni is standing on 18.

To subtract 3 from 18, it has to move 3 steps back

On jumping backwards, Roni Rabbit reaches 15. So, 18 - 3 = 15

3. Subtraction by Backward Counting:

Shreya has 9 muffins. She gives 5 to his brother. How many muffins are left with Shreya.

Start from 9 and count 5 numbers backward.



Let us take one more example.

Start from 20 and count 9 numbers backward 20 - 9 = 11

4. Subtraction by striking out:

Suppose, Shelly has 6 basket balls. Out of which she lost two balls. How many balls are left with her now?

5. Subtraction of zero from a number:

Vineet has seven ice-creams. He gave nothing to his friend. Now how many ice creams does Vineet has?

7 – 0 = 7

On subtracting zero from a number, we get the number itself.

On subtracting 1 from a number, we get the number just before it.

MENTAL ARITHMETIC

Can you add or subtract numbers without using a paper, pen or calculator? You can do this by using your fingers!

Let us add and subtract two numbers using finger pads. We use finger pads (3 in each finger) to count.

Let us understand with the help of an example.

How you will add 5 and 6 on you fingers?

Step 1:     Count 5 pads on fingers.

Step 2:     Now count 6 more pads on the fingers

Step 3:     You will reach at 11

So, you will get 5 + 6 = 11

How to subtract 8 from 18?

Step 1:     Count 18 pads on fingers.

Step 2:     Now count 8 pads backward starting from 18

Step 3:     You will be left with 10 pads

So you get 18 – 8 = 10

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