SOLUTION: This was a question on a practice test that I got wrong and I am not sure what I did wrong. Can you please explain to me how to solve this? It would mean a great deal to me!!
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Question 856145: This was a question on a practice test that I got wrong and I am not sure what I did wrong. Can you please explain to me how to solve this? It would mean a great deal to me!!
What is the sum of the arithmetic sequence 8, 14, 20 …, if there are 22 terms? Found 4 solutions by ewatrrr, richwmiller, Edwin McCravy, AnlytcPhil:Answer by ewatrrr(24785) (Show Source):
You can put this solution on YOUR website! How can we tell you what you did wrong, if you don't show us what you did?
S = ½(2a + (n-1)d)n
S = ½(2*8 + (21)6)22
S = 1562
or another way
Find a22
an = a + (n - 1)d
a22 = 8 + (21)6
a22=134
now find the sum
S = ½(a + an)n
S = ½(8 + 134)22
S = 11(142)
s=1562
You can also use the other formula:
8, 14, 20 …, if there are 22 terms
= the first term which = 8
d = common difference = 2nd term - 1st term = 14 - 8 = 6
check d:
d = common difference = 3rd term - 2nd term = 20 - 14 = 6
So d = 6
n = the number of terms = 22
Substitute , , and
Edwin
You can also use the other formula:
8, 14, 20 …, if there are 22 terms
= the first term which = 8
d = common difference = 2nd term - 1st term = 14 - 8 = 6
check d:
d = common difference = 3rd term - 2nd term = 20 - 14 = 6
So d = 6
n = the number of terms = 22
Substitute , , and
Edwin
