Kanika was given her pocket money on January 1st 2008 she put Rupees 1 on day 1, 2 on Day 2 and rupees 3 on day 3, and continue doing so till the end of the month from this money into her piggy bank, also spend rupees 204 of a pocket money and at the end of the month that she still had rupees hundred with her. How much was her pocket money for the month ?
In a month of Jan , there are 31 days
First term = 1 , Difference = 1
Sum = n / 2 [ 2a + (n - 1)d]
Sum = 31 / 2 [ 2 * 1 + (31 - 1)(1) ]
Sum = 31 / 2 [ 2 + 30 ]
Sum = (31 / 2) * 32
Sum = 31 * 16
Sum = 496
Now this Rs 496 has been put into piggy bank from the pocket money
Let the pocket money be x , also she spent Rs 204 ,Amount Remaining = 100
So , x - 496 - 204 = 100
x - 700 = 100
x = 800
Ans: Rs 800