Question

dar 3 plus 6 plus 9 plus puncte puncte plus 60​

Answer 1

3+6+9+...+60=

=3(1+2+3+....+20)=

=3×(20×21)/2=

=3×10×21=

=30×21=630

Answer 2

3+6+.....+60

Dam factor comun 3!

1•3+2•3+....+20•3
3•(1+2+3+.....+20)
3•(20+19+18+.....+1)
3•(21+21+21+......+21)
3•(21•20:2)
3•(420:2)
3•120=
=360