Răspuns :
nr termeni =(47-3):4+1=44:4+1=11+1=12
S=3+7+11+.....+47=
=3+(3+4)+(3+8)+....+(3+44)=3*12+(4+8+..+44)=36+4(1+2+..+11)=
=36+4*11*12/2=36+4*66=36+264=300
S=3+7+11+.....+47=
=3+(3+4)+(3+8)+....+(3+44)=3*12+(4+8+..+44)=36+4(1+2+..+11)=
=36+4*11*12/2=36+4*66=36+264=300