Scheme 1 requires cutting 18 mm ÷ 6 mm × 3 = 9 times. The time required for each cutting is: (6 mm ÷ 60%) ÷ 60 seconds × 100% = 0. 1 min. Therefore, the total cutting time is 9 × 0. 1 = 0.9 minutes.
Scheme 2, the total cutting time is 18 mm ÷ 4.5 mm × 4 = 16 times. The time required for each cutting is: (4.5 mm ÷ 80%) ÷ 60 seconds × 100% = 0.09375 minutes. Therefore, the total cutting time is 16 × 0.09375 = 1.5 minutes.
Therefore, the first scheme cuts faster than the second scheme because it always requires shorter cutting time.