Given the arithmetic series a1+a2+a3+a4 a 1 + a 2 + a 3 + a 4 8 + 11 + 14 + 17 + . . + 68 what is the value of sum?

Here the first term, a = 8, common difference, d= 11-8= 3 and the last term , l = 68

So before finding the sum, first we need to find the number of terms, and for that we use the formula

a(n) = a+(n-1)d

68 = 8+(n-1)3

Subtracting 8 from both sides

60 = (n-1)3

Dividing both sides by 3

20=n-1

Adding 1 to both sides

n =21

Now we use the formula of sum of n terms of arithmetic series, which is