# Study plan: Percentages for bookkeeping

- Goal: Understand percentages well enough for the Unit 2 quiz, including “what percent of 80 is 12” and percentage increase.
- Deadline: 2026-04-14
- Time available: 3 hours per week
- Starting point: Jo is comfortable with 50% and 10% in her head but struggles when solving for the percent itself or calculating percentage change.

## Plan

| Session | Topic | Length | Source |
|---|---|---|---|
| 1 | Solving for percent, part, and whole using `part = percent × whole` | 60 min | Unit 2: percentages |
| 2 | Percentage increase and decrease using `(new − old) ÷ old × 100` | 60 min | Unit 2: percentages |
| 3 | Mixed practice and quiz strategy | 60 min | Unit 2: percentages |

## Explanation: Solving for percent when part and whole are known

Percent means per hundred. If you know the part and the whole, you are essentially asking “how many hundredths is this part?” Start from the formula `part = percent × whole`. To find the percent, divide both sides by the whole: `percent = part ÷ whole`. That gives a decimal. Multiply by 100 to turn it into a true percent.

Worked example: What percent of 80 is 12? Here the part is 12 and the whole is 80. `12 ÷ 80 = 0.15`. `0.15 × 100 = 15%`.

## Practice

1. What percent of 80 is 12?
2. Find the part: What is 18% of 250?
3. Find the whole: 30 is 25% of what number?
4. A bookkeeping receipt total went from $140 to $154. What is the percentage increase?
5. An old stock value was $90 and the new value is $72. What is the percentage decrease?

## Answers (keep separate)

1. `12 ÷ 80 = 0.15`; `0.15 × 100 = 15%`.
2. Convert 18% to decimal: `0.18`. Then `0.18 × 250 = 45`.
3. Convert 25% to decimal: `0.25`. Then `30 ÷ 0.25 = 120`.
4. `154 − 140 = 14`. `14 ÷ 140 = 0.1`. `0.1 × 100 = 10%`.
5. `90 − 72 = 18`. `18 ÷ 90 = 0.2`. `0.2 × 100 = 20%`.

## Progress notes

- Right: knows that percent means per hundred and can handle simple 50% and 10% mentally.
- Revisit: rearranging `part = percent × whole` when the missing term is the whole, and keeping the sign straight on percentage decreases.