A) 45
B) 50
C) 60
D) 40
Correct Answer: C
Solution :
Let cost \[C=av+\frac{b}{v}\] According to given question, \[30a+\frac{b}{30}=75\] ?(i) \[40a+\frac{b}{30}=65\] ...(ii) On solving (i) and (ii), we get \[a=\frac{1}{2}\]and\[b=1800\] Now, \[C=av+\frac{b}{v}\]\[\Rightarrow \]\[\frac{dC}{dv}=a-\frac{b}{{{v}^{2}}}\] \[\frac{dC}{dv}=0\Rightarrow a-\frac{b}{{{v}^{2}}}=0\] \[\Rightarrow \]\[\frac{dC}{dv}=0\Rightarrow a-\frac{b}{{{v}^{2}}}=0\] \[\Rightarrow \]\[v=\sqrt{\frac{b}{a}}=\sqrt{3600}\]\[\Rightarrow \]\[v=60\,kmph\]You need to login to perform this action.
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