Question

Efectuati 14 + 15 - 16 + 17 + 18 - 19 + 20 + 21 - 22 + … + 194 + 195 - 196.

Answer 1

Răspuns:

6283

Explicație pas cu pas:

14 + 15 - 16 + 17 + 18 - 19 + 20 + 21 - 22 + … + 194 + 195 - 196 = ?

14+15-16 = 29-16 = 13

17+18-19 = 35-19 = 16

20+21-22 = 41-22 = 19

23+24-25 = 47-25 = 22

...........................................

194+195-196 = 193

Suma initiala devine :

13+16+19+22+.......+193 = (13+193)·[(193-13):3+1] : 2 =

= 206·61:2 = 103·61 = 6283