Notam elefanti - e
Ani consecutivi =elefantil initial ,elefantul initial + 1 ,elefantul initial + 2 ......elefantul initial + 8,
e + e+1 + e+2 + e+3 + e+4 + e+5 + e+6 + e+7 + e+8
Iar cum suma ultimilor 3 =96
=> e+6 + e+7 + e+8 = 96
3e +21 = 96
3e = 96 - 21
3e = 75
e = 75:3
e = 25
=> suma primilor 7 = e + e+1 + e+2 + e+3 + e+4 + e+5
= 25+(25+1)+(25+2)+(25+3)+(25+4)+(25+5)
= 25+26+27+28+29+30
=165