Question

Ache a soma dos multiplos de 5 compreendidos entre 53 e 419

Answer 1

a1= 55

an= 415

r = 5

55 + (n-1).5 = 415

5n - 5 = 415-55 ==> 5n = 360+ 5

5n = 365==> n = 73
============================================

S73 = ( 55+365).5
                  2

S73 = 420.55
             2

S73 = 11.550