What is the sum of the arithmetic sequence 153, 139, 125, …, if there are 22 terms?

132

154

176

198

I got 176 could anyone check?

Question

What is the sum of the arithmetic sequence 153, 139, 125, …, if there are 22 terms?

 132

 154

 176

 198

I got 176 could anyone check?

anonymous · Answer

@AkashdeepDeb  could you check this for me?

akashdeepdeb · Answer

Do you know how to find the sum in an arithmetic sequence? :)

anonymous · Answer

$$a_{n} =a _{1} \left( n-1 \right)d$$ with the arithmetic sequence formula right?

akashdeepdeb · Answer

Yes that is right but th to find the sum of an Arithmetic sequence we use
Sum = n/2 * [2a + (n-1)d]
Gpt it?

anonymous · Answer

I think so, would it be 22/2*[2a+(22-1)14] ?

anonymous · Answer

Im confused as to what the a is

akashdeepdeb · Answer

No, see the question says that the sequence decreases, so..
d = -14
a = 153
TRY PUTTING IN THE VALUES YOU ARE ALMOST THERE!! :)

anonymous · Answer

22/2*[2(153)+(22-1)-14] then?

akashdeepdeb · Answer

Yeah!!! 
Now if you calculate the whole thing 
Your answer should be 132!!!  :)

anonymous · Answer

I was really far off :/ thanks for helping!

akashdeepdeb · Answer

:)