A) 20 yr
B) 25 yr
C) 30 yr
D) 35 yr
Correct Answer: A
Solution :
Let the required time be n years. \[\therefore \]\[5550=135+150+...+n\] terms \[=\frac{n}{2}[2\times 135+(n-1)15]\] \[\Rightarrow \] \[2\times 5550=270n+n(n-1)15\] \[\Rightarrow \] \[740=18n+{{n}^{2}}-n\] \[\Rightarrow \] \[{{n}^{2}}+17n-740=0\] \[\Rightarrow \] \[(n-20)(n+37)=0\] \[\Rightarrow \] \[n=20\,yr\] (\[\because \]\[n\] cannot be negative)You need to login to perform this action.
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