1. Identify the total mass of the mixture: 400 grams. 2. Calculate the mass of Compound X: (2/5) * 400 g = 0.4 * 400 g = 160 g. 3. Calculate the mass of Compound Y: 0.35 * 400 g = 140 g. 4. Sum the masses of Compound X and Y: 160 g + 140 g = 300 g. 5. Subtract this sum from the total mass to find the mass of Compound Z: 400 g - 300 g = 100 g. Why others are wrong: A — This is the correct answer. B — This value results from an error in calculation or conversion. C — This is the mass of Compound Y, not Compound Z. D — This is the mass of Compound X, not Compound Z.

1. Convert the multiplier 2.5 to a fraction: 2.5 is equivalent to 2 and 1/2, or 5/2. 2. Multiply the original amount of flour (2/3 cup) by this fractional multiplier: (2/3) * (5/2). 3. Multiply the numerators and the denominators: (2 * 5) / (3 * 2) = 10/6. 4. Simplify the resulting improper fraction: 10/6 = 5/3. 5. Convert the improper fraction to a mixed number: 5/3 = 1 and 2/3 cups. Why others are wrong: A — Correct calculation. B — This would be the result if the baker only multiplied by 2 (the whole number part of 2.5) instead of 2.5. C — This result would occur if the multiplier 2.5 was incorrectly interpreted as 2.25 (or 2 1/4), leading to (2/3) * (9/4) = 18/12 = 1 1/2. D — This would be the result if the baker incorrectly divided 2.5 by 2/3 (2.5 / (2/3) = 5/2 * 3/2 = 15/4 = 3 3/4) instead of multiplying.

1. Convert the decimal portion completed on Tuesday to a fraction: 0.35 = 35/100. 2. Simplify the fraction: 35/100 = 7/20. 3. Add the fraction completed on Monday (3/8) and the fraction completed on Tuesday (7/20). 4. Find a common denominator for 8 and 20, which is 40. 5. Convert 3/8 to 40ths: (3 * 5) / (8 * 5) = 15/40. 6. Convert 7/20 to 40ths: (7 * 2) / (20 * 2) = 14/40. 7. Sum the completed portions: 15/40 + 14/40 = 29/40. This is the total fraction of the order completed. 8. To find the fraction that still needs to be completed, subtract the completed portion from the total order (represented as 1 or 40/40): 40/40 - 29/40 = 11/40. Why others are wrong: B — This is the total fraction of the order that has been completed, not the fraction that still needs to be completed. C — This is the difference between the two completed portions (0.35 - 3/8, or 14/40 - 15/40 if absolute value) rather than their sum or the remaining portion from the whole. D — This could result from an incorrect conversion of 0.35 (e.g., to 2/5, which is 0.4) followed by calculating the remaining portion (1 - (3/8 + 2/5) = 1 - (15/40 + 16/40) = 1 - 31/40 = 9/40).

1. Convert the decimal portion to a fraction: 0.3 = 3/10. 2. Identify the total allocated fraction: Equipment (1/4) + Personnel (3/10). 3. Find a common denominator for 4 and 10, which is 20. 4. Convert fractions to the common denominator: 1/4 = 5/20 and 3/10 = 6/20. 5. Sum the allocated fractions: 5/20 + 6/20 = 11/20. 6. Calculate the remaining portion for contingencies: Total budget (represented as 1 or 20/20) - Allocated portions = 20/20 - 11/20 = 9/20. Why others are wrong: B — This fraction represents the total portion of the budget *allocated* to equipment and personnel, not the remaining portion. C — This would be the result if 0.3 was incorrectly interpreted as 3/5 (which is 0.6), leading to 1 - (1/4 + 3/5) = 1 - (5/20 + 12/20) = 1 - 17/20 = 3/20. D — This would be the result if only the 0.3 (personnel) portion was subtracted from the total, ignoring the 1/4 (equipment) portion (1 - 0.3 = 0.7 = 7/10).

1. Calculate the amount of sand used in the first phase: (2/5) * 25 tonnes = 10 tonnes. 2. Calculate the amount of sand remaining after the first phase: 25 tonnes - 10 tonnes = 15 tonnes. 3. Calculate the amount of sand used in the second phase: 0.6 * 15 tonnes = 9 tonnes. 4. Calculate the amount of sand left after the second phase: 15 tonnes - 9 tonnes = 6 tonnes. 5. Expressing this as a decimal gives 6.0 tonnes. Why others are wrong: A — Correct option. B — This is the amount of sand remaining after only the first phase. C — This is the amount of sand used in the first phase. D — This is the amount of sand used in the second phase.