Question

50+55+.....355+360
Va rog, am nevoie pas cu pas. Mulțumesc.

Answer 1

5(10+11+......+72)

aplicam suma lui Gauss

=>5{(1+2+....+72)-(1+2+...+9)}

(1+2+...+72)= 72×(72+1) /2

= 2628

(1+2+...+9)= 9×(9+1) /2

= 45

=> 5(2628-45)=5×2583=12915