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Question
In a ‘Mahila Bachat Gat’, Kavita invested from the first day of month ₹ 20 on first day, ₹ 40 on second day and ₹ 60 on third day. If she saves like this, then what would be her total savings in the month of February 2020?
Solution
2020 is a leap year.
In February month there are 29 days.
n = 29
On the first day of the month Kavita invested ₹20.
On the second day, she invested ₹40.
On the third day, she invested ₹60.
Kavita's investment is in A.P. 20, 40, 60, ....
a = 20, n = 29, d = 20
Now, `S_n = n/2 [2a + (n - 1)d]`
∴ `S_29 = 29/2 [2(20) + (29 - 1)(20)]`
= `29/2 [40 + 28 xx 20]`
= `29/2 [40 + 560]`
= `29/2 [600]`
= 29 × 300
= 8700
∴ Total savings of Kavita in the month of February 2020 is ₹ 8,700.
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