Question

determinar a soma dos múltiplos de 5 compreendidos entre 7 e 121​

Answer 1

P.A (10,15... 120)

aₙ=a₁+(n-1)r

120=10+(n-1).5

120=10+5n-5

5n+5=120

5n=120-5

5n=115

n=115/5

n=23

Sₙ=n(a₁+aₙ) /2

S₂₃=23(a₁+a₂₃)/2

S₂₃= 23(10+120)/2

S₂₃=(23.130)/2= 23.65=1495

Answer 2

resolucao!

an = a1 + ( n - 1 ) r

120 = 10 + ( n - 1 ) 5

120 = 10 + 5n - 5

120 = 5 + 5n

120 - 5 = 5n

115 = 5n

n = 115/5

n = 23

Sn = ( a1 + an ) n / 2

Sn = ( 10 + 120 ) 23 / 2

Sn = 130 * 23 / 2

Sn = 65 * 23

Sn = 1495