This question tests percent increase in the amount of flour for a recipe. Percent increase is defined as the increase divided by the original base amount, multiplied by 100%. The increase is 15% of 200 grams, so 0.15 × 200 = 30 grams added. The new amount is 200 + 30 = 230 grams. This is correct because the percentage is applied to the original as specified. A common incorrect choice like 215 adds only 7.5% mistakenly. Another error, such as 200, ignores the increase entirely.

This question tests calculating what percent an increase represents of the original value. Percent change is defined as (change ÷ original) × 100%, with the original score as the base. The score increases from 70 to 84, an increase of 14 points. The percent increase relative to the original score is (14 ÷ 70) × 100% = 20%. The correct answer is 20%. A common error is to calculate 14% by looking at the absolute numbers without properly dividing by the base.

This question tests multiple sequential percent changes with different bases. Each percent change uses the previous month's value as its base. January sales: 120 copies. February sales are 30% fewer: 120 × 0.70 = 84 copies. March sales are 25% more than February: 84 × 1.25 = 105 copies. The bookstore sold 105 copies in March. A common mistake is to apply both percentages to the January amount or to incorrectly combine the percentages.

This question tests compound percent change, where multiple percent changes are applied sequentially. When calculating percent change, each percentage is based on the value at that stage, not the original. First, revenue increases by 20% from $500,000: $500,000 × 1.20 = $600,000. Then it decreases by 10% from this new amount: $600,000 × 0.90 = $540,000. The final revenue is $540,000. A common mistake is to combine the percentages incorrectly, such as thinking +20% - 10% = +10% overall, which would incorrectly yield $550,000.

This question tests percent change, specifically a percent decrease from an original value. Percent change is calculated as (change ÷ original) × 100%, where the original value serves as the base. The store starts with 200 jackets and experiences a 15% decrease, so the decrease amount is 0.15 × 200 = 30 jackets. Therefore, the new number of jackets is 200 - 30 = 170 jackets. The correct answer is 170. A common error would be to calculate 15% of some other value or to add instead of subtract the change.

This question tests compound percent change where gains and losses are applied sequentially. Each percent change uses the current value as its base, not the original. Starting with $10,000, a 10% decrease gives: $10,000 × 0.90 = $9,000. Then a 10% increase on this amount gives: $9,000 × 1.10 = $9,900. The final value is $9,900. A common misconception is that a 10% decrease followed by a 10% increase returns to the original value, but this is false because the bases differ.

This question tests sequential percent changes: first a price increase, then a percentage discount on the new price. The price increases from $30 to $36 (a $6 or 20% increase). Then a 10% discount is applied to the new price of $36. The discount amount is 0.10 × $36 = $3.60. Subtracting this from $36 gives the final price: $36 - $3.60 = $32.40. The final advertised price is $32.40. A common error would be to apply the 10% discount to the original $30 price or to miscalculate the discount amount.

This question tests successive percent changes where increases and decreases of the same percentage don't cancel out. Percent change uses the current value as the base for each calculation. Starting with $2,000, a 10% increase gives us $2,000 + 0.10($2,000) = $2,200. Then a 10% decrease from this new base gives us $2,200 - 0.10($2,200) = $2,200 - $220 = $1,980. The final rent is $1,980, which is less than the original $2,000. The key insight is that a 10% decrease from a larger amount ($2,200) removes more dollars than a 10% increase from the original amount ($2,000) added.

This question tests percent change, specifically a percent decrease in the number of backpacks. Percent change is defined as the change amount divided by the original base value, multiplied by 100%. Here, the decrease is 25% of the original 240 backpacks, so the decrease amount is 0.25 × 240 = 60. The new number of backpacks is then 240 - 60 = 180. This result is correct because the percentage decrease is clearly applied to the original stock as stated. A common incorrect choice like 60 fails because it represents only the decrease amount, not the remaining stock. Another error, such as 200, might come from mistakenly subtracting 16.67% instead of 25%, confusing fractions like 1/6 with 1/4.

This question tests calculating the overall percent change after multiple changes to a quantity. Starting with 300 members, a 20% increase adds 0.20 × 300 = 60 members, giving 360 members total. Then 60 members cancel, leaving 360 - 60 = 300 members. The percent change from the original 300 to the final 300 is (300 - 300) / 300 × 100% = 0%. The membership returned to its original level, so the percent change is 0%. The key insight is that the 60 members who joined equals the 60 who left, returning the gym to its original membership count.