Question

Calculati (2+4+6+...+100)-(1+3+5+...+99)

Answer 1

$(2+4+6+...+100)-(1+3+5+...+99) = 50$

$2+4+6+...+100 = | : 2$

$1+2+3+...+50$

$2 \cdot (1+2+3+...+50) =$

$2\cdot50\cdot(50+1):2 = 100\cdot 51:2 = 50\cdot51=2550$

$1+3+5+...+99=$

$100\cdot50:2= 5000 : 2 = 2500$

$2550 - 2500 = 50$