Addition and subtraction within 100 are concepts taught in second-grade math classes. These operations form the foundation of all natural sciences, making it crucial to master and practice them extensively. For young children, counting can seem overly abstract, so Mathema has prepared materials with explanations to help children grasp addition and subtraction within 100.
Online math tutors for second graders can assist children in understanding and mastering the principles of adding and subtracting numbers within 100. Explore the tutor section to meet the educators at Mathema.
Addition Without Regrouping
Simple addition examples within 100 do not require regrouping. These involve using round numbers, such as 10, 20, 30, 40, and so on. Starting with these simple examples can help build a solid foundation for addition within 100.
Round numbers are those that end in zero: 10, 20, 30, 40, 50, 60, 70, 80, 90…
Let’s try a simple example with round numbers. The picture shows apples and plums. Count separately how many apples and plums are in the picture.
So, there are 10 apples and 20 plums in the picture. Now calculate the total number of fruits in the picture.
A simple way to explain this example to a child is by using tens. One ten is 10, two tens are 20, three tens are 30, and so on. There was one ten of apples and two tens of plums in the picture. Therefore, 1 + 2 = 3 tens of fruits. And as we know, three tens is thirty. Ask the child to solve a few similar examples:
Addition With Regrouping
Regrouping is needed when a number in the addition problem is not a round number. In such cases, we break it down into a ten and some units. For example, 12 can be broken down into 10 and 2, and 25 into 20 and 5. Let’s consider an example:
The picture shows 12 pink candies and 9 green candies. To find the sum, we need to break down 12 into 10 and 2. This gives us 10 + 2 + 9. Now add 9 + 2 = 11. This gives us 10 + 11. Now break down 11 into 10 + 1. This gives us 10 + 10 + 1 = 21.
Let’s solve a more complex problem with coins. “Peter has 26 coins. His friend Vasily has 38 coins. How many coins do the boys have together?”
We’ve established that when adding tens, we add tens to tens and units to units. When adding in parts, we write the second addend as a sum. The number 26 has 2 tens and 6 units, so we can write it as a sum of 20 + 6. The number 38 has 3 tens and 8 units, so we can write it as a sum of 30 + 8.
Large numbers should be broken down into tens and units. Add tens to tens and units to units. Practice with children; sometimes, understanding addition within 100 requires a lot of counting.
Subtraction Without Regrouping
Subtraction without regrouping is similar to addition, except for the subtraction operation itself. It is a familiar operation to children, so it can be explained similarly. Here’s an example that can be used:
There were 20 carrots, and the bunny ate 10 of them. How many carrots are left?
Subtraction With Regrouping
To learn subtraction with regrouping, children need to learn to break numbers down into smaller parts. For example, 5 can be broken down into 2 and 3, and 15 into 10 and 5. Let’s consider an example:
There were 45 ants in the anthill. 26 of them went hunting. How many ants are left in the anthill?
To find out how many ants are left, we need to write an expression – subtract the number of ants that went hunting from the total number of ants.
Examples
Problem 1
There were 64 bees in the hive. 14 of them flew out to collect honey. How many bees are left in the hive?
Problem 2
Oleg had 27 candies, and Anya had 35. How many candies do Oleg and Anya have together?
Problem 3
The bunny had 28 carrots. He ate 11 of them. How many carrots are left for the bunny?
Problem 4
Count all the examples in the picture.
