Question

The sum of series 5 + 13 + 21 +.............+181 is ______

Answer 1

Ap

a = 5

d = 13-5=8

$a_n = 181$

So

$a_n = a+ (n-1)d \\ \\ 181 = 5 + ( n-1)8 \\ \\ \frac{176}{8} = n-1 \\ \\ n= 22+1 \\ \\ n=23$

$sum = \frac{n}{2} ( a + a_n)\\ = \frac{23}{2} (5+181) \\ =23 \times 93 \\=2,139$

Answer 2

Answer: 5+13+21+......….....+181

a=5

d=8

l=a+(n-1)d

181=5+(n-1)8= 181-5=(n-1)8=176=(n-1)8

(n-1)=176/8=22

n-1=22

n=22+1=23

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

Sn=23/2[2(5)+(23-1)8]

=23/2[10+22(8)]

=23/2[10+176]

=23/2(186)

=23*22=2159

Step-by-step explanation: