Information given:- 20 machines, each working at a different constant rate
- Each day, exactly 2 machines work, no pair repeats
- After all unique pairs have worked once, the 20 machines then work together for 6 more days to finish the job
Question:- If all 20 machines had worked together from the beginning, how many days total would the job have taken?
Solution:- First, calculate how many unique pairs you can make with 20 machines
- Number of pairs: (20 * 19) / 2 = 380 / 2 = 190
- Therefore, the 'pairs phase' lasts 190 days (190 pairs, 1 pair/day)
- Suppose each machine's rate = 1 unit
- Any pair working = 2 units/day
- All 20 machines together = 20 units/day
- During pairs phase: 190 x 2 = 380 units
- During final phase: 6 x 20 = 120 units
- Total units = 380 + 120 = 500
- If all 20 machines had worked together from the start, total days: 500 / 20 = 25 days
Answer: B, 25 daysBunuel
20 machines, each working at a different constant rate, work to complete a certain job. Each day, exactly 2 machines are assigned to work, and no pair of machines works together more than once. After all such unique pairs have worked once, all 20 machines work together for 6 additional days to complete the job. If all 20 machines had worked together from the beginning, in how many days would the job have been completed?
A. 19
B. 25
C. 26
D. 190
E. 196