Worked Examples: SAT Strategy
Example 1: Easy (Successive Percentages Trap)
Question: A television is originally priced at $\$500$. The store increases the price by $20%$. A month later, the store puts the television on sale for $20%$ off the new price. What is the final price of the television?
SAT Strategy: Do not assume the price goes back to $\$500$! A $20%$ decrease on a larger number removes more value than a $20%$ increase added to a smaller number. Chain your decimal multipliers.
- Start with the original price: $500$.
- Multiply by the $20%$ increase factor ($1 + 0.20$): $500 \times 1.20 = 600$.
- Multiply the new price by the $20%$ decrease factor ($1 - 0.20$): $600 \times 0.80$.
- Calculate the final price: $480$.
- Answer: $480$.
Example 2: Medium (Translating "p% greater than")
Question: $210$ is $p%$ greater than $30$. What is the value of $p$?
SAT Strategy: Translate the English sentence directly into an algebraic equation using the multiplier structure: $\text{New} = \text{Original} \times (1 + \frac{p}{100})$.
- Set up the equation: $210 = 30(1 + \frac{p}{100})$.
- Divide both sides by $30$: $7 = 1 + \frac{p}{100}$.
- Subtract $1$ from both sides: $6 = \frac{p}{100}$.
- Multiply by $100$: $p = 600$.
- (Check: $100%$ of 30 is 30. $600%$ of 30 is 180. $30 + 180 = 210$).
- Answer: $600$.
Example 3: Hard (Conditional Probability in Two-Way Tables)
Question:
{|l|c|c|c|}
&
Algebra &
Geometry &
Total
Juniors & 45 & 15 & 60
Seniors & 10 & 30 & 40
Total & 55 & 45 & 100
If a student is selected at random from those who take Geometry, what is the probability that the student is a Senior?
SAT Strategy: Identify the "condition." The phrase "from those who take Geometry" restricts your entire universe to the Geometry column. Ignore the rest of the table!
- Find the denominator: The total number of students taking Geometry is $45$.
- Find the numerator: Of those $45$ students, how many are Seniors? $30$.
- Form the probability fraction: $\frac{30}{45}$.
- Simplify the fraction (divide by 15): $\frac{2}{3}$.
- Answer: $\frac{2}{3}$.
Practice Questions
Level 1: Easy (Foundational SAT)
- What is $20%$ of $440$? (Grid-in)
- Out of $300$ seeds that were planted, $80%$ sprouted. How many of these seeds sprouted?
- A) $24$
- B) $80$
- C) $240$
- D) $280$
- A pair of shoes originally costs $\$80$. If the shoes are on sale for $25%$ off, what is the sale price of the shoes?
- A) $\$20$
- B) $\$55$
- C) $\$60$
- D) $\$100$
- In a poll of $200$ voters, $130$ voted for Candidate A and the rest voted for Candidate B. What percentage of the polled voters voted for Candidate B? (Grid-in)
-
{|l|c|c|c|}
& Right-Handed & Left-Handed & Total
Male & 42 & 8 & 50
Female & 45 & 5 & 50
Total & 87 & 13 & 100
Based on the table above, what is the probability of randomly selecting a female who is left-handed from the entire group?
- A) $\frac{5}{100}$
- B) $\frac{5}{50}$
- C) $\frac{5}{13}$
- D) $\frac{13}{100}$
Level 2: Medium (Standard SAT)
- A store purchases a jacket from a supplier for $\$40$. The store marks up the price by $50%$ to sell to customers. During a clearance sale, the store discounts the jacket by $20%$ off the selling price. What is the clearance price of the jacket?
- A) $\$48$
- B) $\$52$
- C) $\$58$
- D) $\$60$
- $72$ is $p%$ of $120$. What is the value of $p$? (Grid-in)
- The price of a plane ticket increased by $15%$ from March to April. If the ticket cost $\$345$ in April, what was the price of the ticket in March?
- A) $\$293.25$
- B) $\$300.00$
- C) $\$330.00$
- D) $\$396.75$
-
{|l|c|c|c|}
& Cat & Dog & Total
Has a Yard & 12 & 38 & 50
No Yard & 24 & 6 & 30
Total & 36 & 44 & 80
Based on the table, if a person who owns a dog is chosen at random, what is the probability that this person has a yard? (Grid-in) - A number $x$ is increased by $25%$ to get $y$. Then, $y$ is decreased by $40%$ to get $z$. If $z = 60$, what is the value of $x$? (Grid-in)
Level 3: Hard (Advanced SAT)
- The regular price of a shirt at a store is $\$11.70$. The sale price of the shirt is $80%$ less than the regular price, and the sale price is $30%$ greater than the store's cost for the shirt. What was the store's cost, in dollars, for the shirt? (Grid-in)
- $150$ is $p%$ greater than $40$. What is the value of $p$? (Grid-in)
- In a company, $60%$ of the employees are female, and $40%$ are male. If $30%$ of the female employees and $25%$ of the male employees take the bus to work, what percentage of ALL employees take the bus to work?
- A) $27.5%$
- B) $28%$
- C) $55%$
- D) $58%$
-
{|l|c|c|c|}
& Passed & Failed & Total
Studied & $x$ & 10 & 90
Did not Study & 15 & $y$ & 60
Total & 95 & 55 & 150
According to the partially completed table above, what is the value of $x - y$? (Grid-in) - If $a$ is $50%$ of $b$, and $b$ is $120%$ of $c$, what percentage of $c$ is $a$?
- A) $60%$
- B) $70%$
- C) $170%$
- D) $240%$
Level 4: Very Hard (Slightly beyond SAT)
- The price of an investment portfolio decreases by $x%$ in Year 1. In Year 2, the portfolio's new value increases by $2x%$. If the value of the portfolio at the end of Year 2 is exactly equal to its original value before Year 1, and $x > 0$, what is the value of $x$? (Grid-in)
- A population of a town increased by $p%$ from 2010 to 2015, and then decreased by $p%$ from 2015 to 2020. If the town's population in 2020 was $9% $ less than its population in 2010, what is the value of $p$? (Grid-in)
- In a certain survey, $70%$ of respondents answered "Yes" to Question 1. Of those who answered "Yes" to Question 1, $40%$ answered "Yes" to Question 2. If exactly $140$ respondents answered "Yes" to BOTH questions, how many total people responded to the survey?
- An electronics retailer buys a computer for $C$ dollars. The retailer marks up the price by $25%$ to create the list price. Later, the retailer offers a discount of $d%$ off the list price. If the discounted price is exactly $10%$ less than the original cost $C$, what is the value of $d$? (Grid-in)
- The total cost of an item, including an $8%$ sales tax, is $\$135$. A customer returns the item and receives a full refund, but the store charges a $15%$ restocking fee based on the item's price before tax. How much money, in dollars, does the store keep as a restocking fee? (Grid-in)
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