## Algebra rules
**Remember in the second grade when your teacher** asked you to fill in the box in a problem like this: | 4 + ⬜ = 10 |
**In algebra all we do is use a letter, like "X" instead of a box: ** | 4 + X = 10 |
This **equation** asks you: What number equals 10 when you add 4 to it?
The answer to this question is 6, because 4 + 6 = 10.
**
Here are some simple equations:
**Equation | The
question it asks | The answer | Reason |
---|
**X + 5 = 15** |
**If you add 5 to my number you get 15. What is my number?** |
** X = 10** |
**Because 10 + 5 = 15** |
**X - 13 = 13** |
**If you subtract 13 from my number you get 13. What is my number?** |
** X = 26** |
**Because 26 - 13 = 13** |
** 3X = 18** |
**If you multiply my number by 3, you get 18. What is my number?** |
** X = 6** |
**Because 3 times 6 = 18** |
** X/4 = 5** |
**If you divide my number by 4, you get 5. What is my number?** |
** X = 20** |
**Because 20/4 = 5** |
How about something more complex, like this equation: 2X - 5 = 11 Here's how you solve an equation of this type:
**1. Cover up the "2X" with your finger (I'll use a box): ** | ** ⬜ - 5 = 11** |
**2. Now solve for the value of the "box":** | **
⬜ = 16 because 16 - 5 = 11** |
**3. Now look at what is in the ⬜ :** | **
2X = ⬜ = 16** |
**4. Now solve the above easy equation:** | **
X = 8, because 8 times 2 = 16** |
Here are some other equations, and how you would solve them:
Equation |
Step 1: Cover up the term with X in it |
Step 2: Solve for the boxed term |
Step 3: Look at what's in the box and solve for it |
---|
**3X + 1 = 7** |
** ⬜ + 1 = 7** |
**⬜ = 6
because 6 + 1 = 7** |
**3 X = the ⬜ which is 6,** so X = 2, because 3 X 2 = 6 |
**X/2 - 1 = 3** |
**⬜ - 1 = 3** |
**⬜ = 4
because 4 - 1 = 3** |
**X/2 = the ⬜ which is 4,** so X = 8, because 8/2 = 4 |
**Now, here's a problem for you: 4 X + 7 = 19 X = _______
** |