This is a multi-step percentage question testing sequential operations. Choice C ($100.00) is correct — let P = original price. After 20% discount: P × 0.80. After 10% tax on the discounted price: P × 0.80 × 1.10 = P × 0.88. Set equal to $88: P × 0.88 = 88 → P = $100. Choice A ($80.00) undoes only the tax but not the discount: $88 ÷ 1.10 = $80 — finding the pre-tax discounted price rather than the original price. Choice B ($96.00) undoes only the discount but not the tax: $88 ÷ 0.80 = $110... wait — that gives $110. $96 may come from $88 + 10% − 2% = various errors. Choice D ($120.00) applies a single combined reversal incorrectly, possibly computing $88 ÷ 0.80 + tax error. Pro tip: Work backwards through sequential percentage changes. The final price $88 = original × 0.80 × 1.10. To find the original, divide by BOTH factors: $88 ÷ (0.80 × 1.10) = $88 ÷ 0.88 = $100. Never undo just one of the percentage operations.

We need to find the percent increase from $50 to $60. Percent change is calculated as (new value - original value)/original value × 100. Here: ($60 - $50)/$50 × 100 = $10/$$\50$$ × 100 = 0.2 × 100 = 20%. Choice B incorrectly calculates 10/60 instead of 10/50.

This question asks us to convert $75%$ to a decimal. To convert a percent to a decimal, divide by 100 or move the decimal point two places left. Calculate: $75% \div 100 = 0.75$. Choice C (0.075) represents the common error of moving the decimal point three places instead of two.

This question asks us to find 40% of 300. To find a percent of a number, convert the percent to a decimal and multiply: $40% = 0.40$. Calculate: $0.40 \times 300 = 120$. Choice B (150) might result from incorrectly calculating 50% of 300 instead of 40%.

This question asks for the sale price after a 30% discount on a $50 shirt. First find the discount amount: 30% of $50 = 0.30 × $50 = $15. Then subtract from the original price: $50 - $15 = $35. Choice A ($15) incorrectly gives just the discount amount rather than the final sale price.

We need to find the simple interest earned on $500 at 10% for one year. Simple interest is calculated as Principal × Rate × Time. Here: $500 × 0.10 × 1 = $50. Choice A ($5) uses 1% instead of 10%, and choice C ($$\450$$) appears to subtract the interest from the principal.

This question asks for 20% of 150. To find a percent of a number, convert the percent to a decimal by dividing by 100, then multiply by the number. $20% = 20 \div 100 = 0.20$, so $0.20 \times 150 = 30$. Choice B incorrectly calculated $20 \times 150 \div 100$ in the wrong order, while choice C mistakenly used $150 \div 2$.

This question asks us to find 30% of 90. To find a percent of a number, convert the percent to a decimal and multiply: $30% = 0.30$. Calculate: $0.30 \times 90 = 27$. Choice B (30) represents the error of confusing the percent value with the result.

We need to find the total cost of a $40 shirt with 8% sales tax. The tax amount is 8% of $40 = 0.08 × $40 = $3.20. The total cost is the original price plus tax: $40 + $3.20 = $43.20. Choice C ($40.08) incorrectly calculates as if the tax were $0.08, not $3.20.

We need to convert 75% to a fraction in simplest form. First write 75% as 75/100, then simplify by finding the greatest common factor: 75/100 = (75÷25)/(100÷25) = 3/4. Choice A (75/100) is not in simplest form, and choices C and D represent values greater than 1.