Math worksheet on percent increase and decrease with real-world application problems.

Problem Analysis:

The image contains four problems related to percent increase and decrease. Below, I will solve each problem step by step and explain the solution.

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Problem 1: Percent Increase in Baby's Weight

Question:
A baby weighed 8.6 lbs when it was born. After one month, the baby weighed 10 lbs. What was the percent increase in the baby's weight after one month? (Round to the nearest whole percent.)

#### Solution:
1. Identify the initial and final weights:
- Initial weight = 8.6 lbs
- Final weight = 10 lbs

2. Calculate the increase in weight:
\[
\text{Increase in weight} = \text{Final weight} - \text{Initial weight} = 10 - 8.6 = 1.4 \, \text{lbs}
\]

3. Calculate the percent increase:
The formula for percent increase is:
\[
\text{Percent Increase} = \left( \frac{\text{Increase in weight}}{\text{Initial weight}} \right) \times 100
\]
Substituting the values:
\[
\text{Percent Increase} = \left( \frac{1.4}{8.6} \right) \times 100
\]

4. Perform the calculation:
\[
\frac{1.4}{8.6} \approx 0.1628
\]
\[
0.1628 \times 100 \approx 16.28
\]

5. Round to the nearest whole percent:
\[
16.28 \approx 16
\]

#### Final Answer for Problem 1:
\[
\boxed{16}
\]

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Problem 2: Lake Depth Decrease Due to Drought

Question:
A lake had a depth of 11.1 feet at the beginning of July. Throughout the month, the lake's depth decreased by 23% due to drought. By the end of July, what was the depth of the lake?

#### Solution:
1. Identify the initial depth and the percentage decrease:
- Initial depth = 11.1 feet
- Percentage decrease = 23%

2. Calculate the decrease in depth:
The formula for the decrease is:
\[
\text{Decrease in depth} = \left( \frac{\text{Percentage decrease}}{100} \right) \times \text{Initial depth}
\]
Substituting the values:
\[
\text{Decrease in depth} = \left( \frac{23}{100} \right) \times 11.1
\]

3. Perform the calculation:
\[
\frac{23}{100} = 0.23
\]
\[
0.23 \times 11.1 = 2.553
\]

4. Calculate the final depth:
\[
\text{Final depth} = \text{Initial depth} - \text{Decrease in depth} = 11.1 - 2.553 = 8.547
\]

5. Round to the nearest hundredth (if necessary):
\[
8.547 \approx 8.55
\]

#### Final Answer for Problem 2:
\[
\boxed{8.55}
\]

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Problem 3: Percent Off on a Hat

Question:
A hat originally costs $35. You pay $25. What percent off was the hat?

#### Solution:
1. Identify the original price and the price paid:
- Original price = $35
- Price paid = $25

2. Calculate the discount amount:
\[
\text{Discount amount} = \text{Original price} - \text{Price paid} = 35 - 25 = 10
\]

3. Calculate the percent off:
The formula for percent off is:
\[
\text{Percent Off} = \left( \frac{\text{Discount amount}}{\text{Original price}} \right) \times 100
\]
Substituting the values:
\[
\text{Percent Off} = \left( \frac{10}{35} \right) \times 100
\]

4. Perform the calculation:
\[
\frac{10}{35} \approx 0.2857
\]
\[
0.2857 \times 100 \approx 28.57
\]

5. Round to the nearest whole percent:
\[
28.57 \approx 29
\]

#### Final Answer for Problem 3:
\[
\boxed{29}
\]

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Problem 4: Cost of Meal with Tip

Question:
You buy a salad and soup at the 99 Restaurant for $9. You leave an 18% tip. How much do you pay for the meal and tip?

#### Solution:
1. Identify the cost of the meal and the tip percentage:
- Cost of the meal = $9
- Tip percentage = 18%

2. Calculate the tip amount:
The formula for the tip is:
\[
\text{Tip amount} = \left( \frac{\text{Tip percentage}}{100} \right) \times \text{Cost of the meal}
\]
Substituting the values:
\[
\text{Tip amount} = \left( \frac{18}{100} \right) \times 9
\]

3. Perform the calculation:
\[
\frac{18}{100} = 0.18
\]
\[
0.18 \times 9 = 1.62
\]

4. Calculate the total cost (meal + tip):
\[
\text{Total cost} = \text{Cost of the meal} + \text{Tip amount} = 9 + 1.62 = 10.62
\]

#### Final Answer for Problem 4:
\[
\boxed{10.62}
\]

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Final Answers:

1. \(\boxed{16}\)
2. \(\boxed{8.55}\)
3. \(\boxed{29}\)
4. \(\boxed{10.62}\)