有位学生在网上论坛提出这道数学题,寻求帮助。我看了一看,心里也“痒”了,就尝试回答这道问题。我把解答步骤贴在此,希望有兴趣的学生也可从此网站学习高级数学。
A rectangular tank can be filled with water by 2 pipes in 6 minutes. If the larger pipe alone takes 5 minutes less to fill the tank than the smaller pipe, find the possible time each pipe will take to fill the tank. (Hint: use the concept of rate of flow.)
V = volume of tank
T = time for smaller pipe to fill the tank
L = rate of flow for larger pipe
S = rate of flow for smaller pipe
A rectangular tank can be filled with water by 2 pipes in 6 minutes:
V = (L+S) X 6
V = 6V + 6S ——– (1)
If the larger pipe alone takes 5 minutes less to fill the tank than the smaller pipe:
V = ST
S = V/T——– (2)
V = L(T-5)
L = V/(T-5) ——- (3)
Substitute (2) and (3) into (1)
V = 6V/(T-5) + 6V/T
Divide by V
1 = 6/(T-5) + 6/T
1-6/T = 6/(T-5)
(T-6)/T = 6/(T-5)
(T-6)(T-5) = 6T
T^2-11T+30 = 6T
T^2-17T+30 = 0
(T-15)(T-2) = 0
T = 15 or T = 2
because T>5, therefore T = 15.
Therefore, time for smaller pipe is 15 minutes and time for larger pipe is 10 minutes.
No comments:
Post a Comment