Give and Take
Math is a part of everyday life, whether counting money, sharing toys, or solving problems! Explore the core operations of **Addition (Give)** and **Subtraction (Take)** using two- and three-digit numbers.
- Select a concept below to explore addition and subtraction rules.
- Learn the **keywords** that signal Addition or Subtraction in a story problem.
- Practice solving word problems using three-digit numbers.
- Use the **Classification** module to sort operation keywords.
- Test your arithmetic skills with the **Practice Quiz** button.
Addition and subtraction are the foundation of mathematical problem-solving. In story problems, keywords like 'total,' 'more,' or 'left' help determine which operation to use.
The Core Operations
Addition is the process of **combining** quantities. When adding two- or three-digit numbers, we start from the **Ones place** and regroup (carry over) when a sum is 10 or more.
| Place | Operation | Example: 125 + 347 |
|---|---|---|
| Ones | 5 + 7 = 12 | Write 2, Carry over 1 to Tens |
| Tens | 1 + 2 + 4 = 7 | Write 7 |
| Hundreds | 1 + 3 = 4 | Write 4. **Answer: 472** |
Subtraction is the process of finding the **difference** between two quantities. We start from the **Ones place** and borrow (regroup) from the next place value when the top digit is smaller than the bottom digit.
Keywords for subtraction: *less, take away, difference, remaining, how many more.*
To successfully solve a word problem, always follow these steps:
- **Read** the problem carefully to understand the situation.
- **Identify** the numbers and the **keyword** that tells you the operation (Add or Subtract).
- **Calculate** the problem, starting with the Ones place.
- **State** the final answer clearly.
Titration of Vinegar
Acid-Base Titration with NaOH and Phenolphthalein
