Answer :

The arithmetic progression is given.
Here first term is 7 and common difference is

Last term l = 84


Let no. of terms be n.
Since, an = a + (n - 1)d


Where,


a = First term of AP
d = Common difference of AP
and no of terms is ‘n’





22 = n – 1
n = 23


Since the sum of n terms is
Sn =

So sum of 23 terms S23
]
= 11.5 [14 + 22 × 3.5]
= 11.5[ 14 + 77]
= 11.5 × (91)
= 1046.5


Hence, Sum is 1046.5 = .


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