Question

A new year resolution ritika planned to save from her pocket money everyday . Starting from 5th Jan , she decided to save amount equal to date of the month . On 30th jan she decided to get a gift for their maids daughter for Rs 50 and a birthday present worth RS.100 for her grandfather. What is the amount left with her at the end of the month ?

Pls specify the ans clearly with appropriate steps..

Answer 1

savings from 5th to 31 Jan:
          5 + 6 + 7 + 8 + ..... + 29 + 30 + 31
          Arithmetic series:  a = 5,  n = 27,  d = 1
         sum = [2*5+ 26*1] 27/2 = 18*27= 486

expenses:  50+100 = 150.

Balance at the end of the month = 486 - 150 = 336.