Question

Find the sum of the arithmetic series 3+8+13+..+438

Answer 1

Answer:

19404

Step-by-step explanation:

sum of arithmetic series is

Sn = n/2 (2a + (n-1)d)

or

Sn = n/2 (a + an)

a = 1st unit

an = last unit

d = difference

8-3 or 13-8 so d = 5

then first step is to find the value of n

an = a + (n-1)d

438 = 3 + (n-1)5

438 - 3 = 5n - 5

435 = 5n - 5

435 + 5 = 5n

440 = 5n

n = 440/5

n = 88

then we can find the sum

Sn = 88/2 (3 + 438)

S88 = 19404