Respostas

2012-12-13T21:38:45-02:00
Sn= (a1+an)*n/2

67500=(a1+an)*15/2 ---> 67500=(a1+a1+14*500)*15/2

67500=(a1+a1+14*500)*15/2

9000=2a1+7000 ---> a1=1000

a3=1000+2*500=2000
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