Question

What is the sum of the arithmetic sequence 5, 11, 17 …, if there are 24 terms?

Answer 1

common difference d = 11-5 = 6

sum of n terms =

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

plug in n = 24, a = 5 and d = 6 to get your answer

Answer 2

i'll tell you a completely different method
first calculate the 24th term..
it will be 5+(23)(6) = 143
now keep adding 1st and last terms,,move from left to right (from beginning) and from right to left ( from end)
i.e. 5+143 = 148
11 + 137 =148
17 + 131 =148
.
.
.
12 times

add all eqns..so your ans is 148*12 !!

Answer 3

you can also see it as sum of n terms = n(first term + last term)/2
or you may use the formulla which cwrw told..its the same thing..

Answer 4

thank youuu!