Problema Solution

Find five consecutive odd numbers that have a sum of 65.

Answer provided by our tutors

Every odd number can be written in a form 2k + 1, where k is integer thus for the five consecutive numbers we can write:


2k - 3, 2k - 1, 2k + 1, 3k + 3, 2k + 5, where k is integer


We need to find k so that the sum of the above numbers is 65 that is


(2k - 3) + (2k - 1) + (2k + 1) + (3k + 3) + (2k + 5) = 65


2k - 3 + 2k - 1 + 2k + 1 + 3k + 3 + 2k + 5 = 65


10k + 5 = 65


10k = 65 - 5


10k = 60


k = 60/10


k = 6


The first odd number will be 2k - 3 = 2*6 - 3 = 9


Indeed 9+11+13+15+17 = 65


The five consecutive odd numbers are 9, 11, 13, 15, 17.