Q9 of 85 Page 104

Find the sum of all odd numbers from 5 to 205.

Formula used.


Sn = [a + l]


an = a + (n–1)d


⇒ The 1st odd number is 5


⇒ The last odd number is 205


⇒ Difference between every odd number is 2


an = a + (n–1)d


205 = 5 + (n–1)2


205 = 5–2 + 2n


2n = 205 – 3


n = = 101


Sn = [a + l]


= [5 + 205]


= 101×105


= 10605


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