This question tests proportions in solutions. The ratio of salt to water is 3:97, total parts 100. For 1,000 grams total, salt is (3/100) × 1,000 = 30 grams. This calculates the mass fraction. Choice A is justified as correct. A distractor like 97 could be misreading the ratio. Adding masses directly might give 300.

This question tests proportions in mixtures. The ratio of nuts to dried fruit is 5:3, total parts 8. For 24 ounces total, dried fruit is (3/8) × 24 = 9 ounces. This finds the portion correctly. Choice B is justified as the answer. A distractor like 15 could be the nuts portion instead. Reversing to 3:5 would give 7.2 ounces fruit.

This question tests ratios in mixtures. The ratio of blue to white paint is 4:1, so total parts are 5. With 3 liters white as 1 part, blue is 4 × 3 = 12 liters, total 15 liters. This scales the ratio to find the whole. Choice B is justified as correct. A distractor like 12 might be the blue amount only. Reversing to 1:4 would give a smaller total like 3.75.

This question tests rates for speed. The cyclist travels 18 km in 45 minutes, which is 0.75 hours, so speed is 18 / 0.75 = 24 km/h. This converts time and divides distance by time correctly. The proportional relationship gives the constant rate. Choice A is justified as the answer. A distractor like 40 might arise from using 45 minutes as 0.45 hours. Forgetting the conversion could lead to 0.4 km/h.

This question tests rates of flow. The pipe fills at 12 gallons per minute, a constant rate. In 25 seconds, or 25/60 = 5/12 minutes, gallons added are 12 × (5/12) = 5. This converts time and applies the rate. Choice A is justified as correct. A distractor like 300 could be from ignoring the time conversion. Using seconds directly might yield small values like 0.48.

This question tests ratios of quantities. The ratio of red to blue marbles is 3:5, meaning for every 3 red, there are 5 blue. With 40 blue marbles corresponding to 5 parts, each part is 40 / 5 = 8 marbles. Thus, red marbles are 3 × 8 = 24. This justifies choice A as correct. A distractor like 15 might result from reversing the ratio to 5:3. Another error could be adding the parts incorrectly, leading to disproportionate calculations.

This question tests ratios in splitting costs. The ratio among Alex, Bri, and Chen is 2:3:5, total parts 10. Chen's 45 dollars is 5 parts, so each part is 45 / 5 = 9 dollars, total bill 10 × 9 = 90 dollars. This scales the ratio to the total. Choice A is justified as correct. A distractor like 75 might come from incorrect part division. Reversing ratios could lead to 225.

This question tests rates of production. The machine produces 180 bolts in 12 minutes, giving a rate of 180 / 12 = 15 bolts per minute. For 50 minutes, the total is 15 × 50 = 750 bolts. This applies the constant rate proportionally over time. Choice A is justified as correct. A distractor like 720 might come from using hours instead of minutes. Incorrectly inverting the rate could lead to choices like 150.

This question tests proportions in scaling. The enlargement multiplies each dimension by 1.5, a proportional increase. Original width 8 inches becomes 8 × 1.5 = 12 inches. This applies the scale factor directly. Choice C is justified as correct. A distractor like 9.5 might come from adding instead of multiplying. Using a different factor like 1.2 could lead to 9.6, close to distractors.

This question tests proportions in mixtures. The ratio of acid to water is 1:9, so acid is 1 part out of total 10 parts. With 500 mL total, acid is (1/10) × 500 = 50 mL. This calculation finds the component volume correctly. Choice A is justified as the answer. A distractor like 450 could be from taking the water portion instead. Reversing the ratio to 9:1 would yield 450 mL acid, a common error.