for an AP first term is -7 and last term is 53 . if the sum of all terms is 483 , then find the number of terms and the common difference
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a=-7
l=53
Sn = 483
Sn =n/2(a+l)=n/2(-7+53)= n/2×46=23n
So, 23n=483
n=21
So, an =53
a+(n-1)d = 53
-7+(21-1)d =53
20d = 60
d=3
Number of terms is 21 and common difference is 3
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