- Choice G
$$a_1=10 $$ $$d=2 $$ $$a_n=10+2(n-1)=2n+8 $$ $$S_n=\frac {a_1+a_n}{2}\cdot n=\frac {10+2n+8}{2}\cdot n=220 $$ $$n=11$$
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$$a_1=10 $$ $$d=2 $$ $$a_n=10+2(n-1)=2n+8 $$ $$S_n=\frac {a_1+a_n}{2}\cdot n=\frac {10+2n+8}{2}\cdot n=220 $$ $$n=11$$
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