The sum of first 5 terms of an ap and the sum of first 7 terms of an ap is 167 if sum of first 10 terms of the ap is 235 find the sum of its first 20 terms
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S5+S7=167
S10=235
S20=?
Sn=2x1.6+(n-1)4.8
Sn= 3.2+(n-1)4.8
= 3.2+4.8n-4.8
4.8n-1.6
S10=235
S20=?
Sn=2x1.6+(n-1)4.8
Sn= 3.2+(n-1)4.8
= 3.2+4.8n-4.8
4.8n-1.6
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