Question

+14+.....+84 find the sums given
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Answer 1

ANSWER

In given series of AP first term a=7, common difference d= 1021−7=221−7=27 and last term l=84

Since, l=a+(n−1)d

⇒84=7+(n−1)27

⇒84−7=(n−1)27

⇒77=(n−1)27

⇒77×72=n−1

⇒22=n−1

⇒n=23

Since, Sn=2n(a+l)

⇒Sn=223(7+84)

⇒Sn=91×223

⇒Sn=22093

⇒Sn=104621