MCQ
In a tour, I spent every day as many ten-rupee notes as the number of days I had been away from the home. My total expenditure was 18,300. How long did I stay away from home?
Options
1 month
2 months
3 months
4 months
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Solution
2 months
Explanation:
Let man spend ₹ 10, 20, 30 ...........
On 1st 2nd 3rd ....... day respectively
ATQ
10 + 20 + 30 .............=18300
`"S"_"n"="n"/2(2"a"+("n"-1)"d")`
`"n"/2(2(10)+("n"-1)10)=18300`
`"n"/2[10"n"+10]=18300`
5n2 + 5n = 18300
n2 + n − 3660 = 0
n2 + 61n − 60n − 3660 = 0
n (n + 61) − 60(n + 61) = 0
(n − 60) (n + 61) = 0, n = 60, n ≠ 61
n = 60
i.e. 2 months
Concept: Series and Equations (Entrance Exam)
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