13+12+23+56+….. hitunglah jumlah deret aritmatika tersebut jika banyak sukunya 11

1/3 + 1/2 + 2/3 + 5/6 + … deret aritmatika, maka

a = 1/3
b = 1/2 – 1/3 = (3-2)/6 = 1/6
n= 11 (diketahui dari soal)

Sn = n/2 [2a + (n-1)b]
S11 = 11/2 [2.1/3 + (11-1)1/6]
S11 = 11/2 [2/3 + 10.1/6]
S11 = 11/2 [2/3 + 10/6]
S11 = 11/2 [2/3 + 5/3]
S11 = 11/2 [7/3]
S11 = 77/6