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### Decimals
- Terms:
- Given the number `9123.456`:
- The **`tenth`** is the `4`
- The **`hundredth`** is `5`
- The **`thousandths`** is `6`
- The **`ones`* is `3`
- The **`tens`** is `5`
- The **`hundreds`** is `1`
- The **`thousands`** is `9`
- **Remember, `tens` and `tenths` may sound the same, but they are `DIFFERENT`!
- To round to a a **`tenth`**, **`hundredth`**, and **`thousandths`**
- The **`tenth`** is the `4`.
- The **`hundredth`** is `5`.
- The **`thousandths`** is `6`.
- The **`ones`** is `3`.
- The **`tens`** is `5`.
- The **`hundreds`** is `1`.
- The **`thousands`** is `9`.
- **Remember, `tens` and `tenths` may sound the same, but they are `DIFFERENT`**!
- To round to a **`tenth`**, **`hundredth`**, and **`thousandths`**
- Tenths
- If the `hundredth` is `5` or higher, round up, else, round down.
- Hundreth
- Example:
- Round `12.53223` to the tenths
- The answer is `12.5`, as the hundredths, or `3` is smaller than 5.
- Hundredth
- If the `thousandth` is `5` or higher, round up, else, round down.
- Example:
- Round `12.53521` to the hundredth
- The answer is `12.4`, as the thousandths, or `5` is bigger or equal to 5.
- Thousandth
- If the number of the `thousandth` is `5` or higher, round up, else, round down.
- If the number of the `thousandth` is `5` or higher, round up, else, round down.
- Example:
- Round `12.5356` to the thousandths
- The answer is `12.536`, as the number after the thousandths, or `6` is bigger than 5.
- To round to a **`ones`**, **`tens`**, **`hundreds`**, and **`thousands`**
- Ones
- If the `tenths` is `5` or higher, round up, else, round down.
- Example:
- Round `123.5333` to the ones
- The answer is `124`, as the tenths, or `5` is bigger than or equal to 5.
- Tens
- If the `ones` is `5` or higher, round up, else, round down.
- Example:
- Round `123.5777` to the tens
- The answer is `120`, as the ones, or `3` is smaller than or equal to 5.
- Hundreds
- If the `tens` is `5` or higher, round up, else, round down.
- Example:
- Round `177.34343` to the hundreds
- The answer is `200`, as the tens, or `7` is bigger than 5.
- Thousands
- If the `hundreds` is `5` or higher, round up, else round down.
- Example:
- Round 566.777` to the thousands
- The answer is `1000`, as the hundreds, or `5` is bigger or equal to 5.
## Integers
### Multiplication and Division
- Pretend `a` and `b` are random positive numbers
|Type|Outcome|
|:---|:------|
|a × b|Positive number|
|a × (-b)|Negative number|
|(-a) × b|Negative number|
|(-a) × (-b)|Positive number|
|a ÷ b|Positive number|
|a ÷ (-b)|Negative number|
|(-a) ÷ b|Negaitve number|
|(-a) ÷ (-b)|Positive number|
- Treat as normal divion and multiplacation, and just add the negative sign infront of the number according to the rules above.
- Practice
- 8 × -7
- Answer: `-56`
- 2 × 4
- Answer: `8`
- -7 × -7
- Answer: `1`
- -10 × 4
- Answer: `-40`
- 8 ÷ 4
- Answer: `2`
- -16 ÷ -8
- Answer: `2`
- -4 ÷ 1
- Answer `-4`
- 9 ÷ -3
- Answer: `-3`
### Addition and Division
- Pretend `a` and `b` are random postive numbers
|Type|Equivalent|
|:---|:---------|
|a+b|a+b|
|b+a|b+a|
|a+(-b)|a-b|
|(-a)+b|b-a|
|a-b|a-b|
|b-a|b-a|
|a-(-b)|a+b|
|(-a)-b|a-b|-(a - b)|
### Order Or Operation
- BEDMAS
- Follow ```BEDMAS``` for order of operations if there are more than one operation
| Letter | Meaning |
|:------:|:-------:|
| B / P | Bracket / Parentheses |
| E | Exponent |
| D | Divison |
| M | Multiplication |
| A | Addition |
| S | Subtraction |
- <img src="https://ecdn.teacherspayteachers.com/thumbitem/Order-of-Operations-PEMDAS-Poster-3032619-1500876016/original-3032619-1.jpg" width="300">
- Follow order of operation, inorder to do know which operation to do first.
- Example: Given $`(2+4) \times 5 - 9 \div 3`$
- First do everything in brackets: $`(6) \times 5 - 9 \div 3`$
- Then do multiplication/division: $`30 - 3`$
- Then finally, do subtaction/addition: $`27`$
- The answer is `27`.
## Fractions / Rational Numbers
- The number on the top is called the `numerator`.
- The number on the bottom is called the `denominator`.
- A fraction in its most simple form is when the `numerator` and `denominator` cannot be both divided by the same number.
### Additions / Subtractions With Fractions
- Example: $`\frac{3}{5} + \frac{4}{3}`$
- Find `common denominator`, which is `15`, as `5` and `3` both are factors of `15`.
- You can do this easily with a table, just count by the number you are using, for example:
- |Counting by 5s | Counting by 3s |
|:--|:--|
|5|3|
|10|6|
|15|9|
|20|12|
|25|15|
- As you can see, both columns contain the number `15`, so `15` is the common denominator.
- Now, after we find the denominator, we must convert the fraction so that it has the `common denominator`. To do this, we must multiply the denominator by a number, so that it equals the `common denominator`. For the first fracion $`\frac{3}{5}`$, the `denominator` is `5`, to get to `15`, we must multiply it by `3`. Now, whatever we do on the bottom, me **MUST** do it on the top too, so we also multiply the `numerator` by `3` as well, the new fraction is now $`\frac{3 \times 3}{5 \times 3} = \frac{9}{15}`$.
- We now do the same thing to the other fraction: $`\frac{4 \times 5}{3 \times 5} = \frac{20}{15}`$
- Now that the denominators are the same and the fractions are converted, we can just simply add the `numerators` together while keeping the `denominator` the same. The result is $`\frac{9 + 20}{15} = \frac{29}{15}`$.
- The same steps applied to subtracion, with the only difference of subtacting the numerators rather than adding them.
### Multiplaction With Fractions
- To multiply a fracion, simply multiply the `numerators` together, and the `denominators` together.
- Example: $`\frac{3}{6} \times \frac{7}{4}`$
- Answer: $`\frac{3 \times 7}{6 \times 4} = \frac{21}{24}`$
### Division With Fractions
- To divide 2 fractions, flip the second fraction upside down.