Question

Metoda guess
2+4+6+.........+140=?

Answer 1

$2 + 4 + 6 + ... + 140$

$= 2(1 + 2 + 3 + ... + 70)$

$= 2 \times \frac{70(70 + 1)}{2}$

$= 70(70 + 1)$

$= 70 \times 71$

$= 4970$