Question

calcule a soma dos múltiplos de 5 entre 24 e 100

Answer 1

a₁ = 25
an = 95
n = ?
r = 5

an = a₁ + (n-1) * r
95 = 25 + (n-1) * 5
95 = 25 + 5n - 5
5n = 95 - 25 + 5
5n = 75
n = 75/5
n = 15

Sn = (a₁ + an) * n / 2
S₁₅ = (25 + 95) * 15 / 2
S₁₅ = 120 * 15 / 2
S₁₅ = 60 * 15
S₁₅ = 900