Correct Answer: B

Rationale: To translate 'Five less than twice the number' into a mathematical expression, you first calculate twice the number (2x) and then subtract 5 from it. This gives you 2x-5. Therefore, choice B, 2x-5, accurately represents the mathematical expression for 'Five less than twice the number.' The phrase 'Five less than' implies subtraction, and 'twice the number' is represented by 2x. Thus, when you subtract 5 from twice the number, the correct expression is 2x-5.

Correct Answer: A

Rationale: To calculate the 15% gratuity on a $38.40 bill, you multiply the bill amount by 0.15 (15%): $38.40 x 0.15 = $5.76. Since gratuity amounts are typically rounded up, the estimated gratuity would be $6.00, making choice A the correct answer. In this case, rounding up to the nearest whole dollar is common practice in gratuity calculations to simplify tipping and ensure a fair amount for the service provided.

Correct Answer: A

Rationale: After spending 80% of $60, Lana spends $48, leaving her with $12. When she invests this remaining amount and earns an 80% profit on $12, it amounts to $21.60 ($12 + 80% of $12 = $12 + $9.60 = $21.60). Therefore, Lana now has $21.60 in total.

Correct Answer: C

Rationale: To convert a fraction to a percentage, divide the numerator by the denominator and then multiply by 100. For the fraction 5/8, it equals 0.625 when divided, which when multiplied by 100 results in 62.50%. Therefore, choice C, 62.50%, is the correct percentage equivalent to the fraction 5/8.

Correct Answer: B

Rationale: The student's pattern involves rounding numbers to the nearest tens or hundreds to simplify calculations. By analyzing the given examples, it is evident that the student tends to round numbers up or down, leading to slight variations from the exact sum. Applying the same strategy to 452 and 5017, we can estimate 450 + 5020 = 5470. Therefore, choice B is the correct estimate for the sum of 452 + 5017.