8.Nine large pipes will drain a pond in eight hours and six small pipes will drain the same pond in sixteen hours. How long will it take 3 large pipes and 5 small pipes to drain the pond?
a. 3 hours and 50 minutes
b. 14 hours and 15 minutes
c. 12 hours and 20 minutes
d. 10 hours and 40 minutes
Interesting Math Question! I
2006-12-12 9:27 pm
回答 (2)
2006-12-12 9:49 pm
✔ 最佳答案
a large pipe will drain a pond in 1/(9x8) =1/72 per houra small pipe will drain a pond in 1/(6x16) =1/96 per hour
For 3 large pipes and 5 small pipes, it take
1/(3x1/72+5x1/96)=1/(1/24+5/96)=1/(96/9)=32/3=10 2/3
ans. is d. 10 hours and 40 minutes
2006-12-12 10:02 pm
Large pipes:
1 large pipe take 9*8 = 72 hrs to drain the pond
Small pipes:
1 small pipe take 6*16 = 96 hrs to drain the pond
For 3 large pipes and 5 small pipes:
1/(3/72 + 5/96) hours = 10.67 hours
2006-12-12 14:03:04 補充：
The answer is d. 10 hours and 40 minutes
1 large pipe take 9*8 = 72 hrs to drain the pond
Small pipes:
1 small pipe take 6*16 = 96 hrs to drain the pond
For 3 large pipes and 5 small pipes:
1/(3/72 + 5/96) hours = 10.67 hours
2006-12-12 14:03:04 補充：
The answer is d. 10 hours and 40 minutes
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