Find the sum of 5+8+11+14+.........+89
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an=a+(n-1)d
89=5+(n-1)3
89=5+3n-3
89=2+3n
n=29
Sn=n/2[2a+(n-1)d]
=29/2[10+84]
=29/2[94]
=29×47
=1363
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