Asked by Jay
The sum of the first 12terms of an arithmetic progression is 135 while the sum of the next 8 terms is 210. Find the common difference
Answers
Answered by
Steve
We are told that
S12 = 135
S20-S12 = 210
S20 - 135 = 210
S20 = 345
Now, we know that
S20 = 20/2 (2a+19d)
S12 = 12/2 (2a+11d)
So, we have
10(2a+19d) = 345
6(2a+11d) = 135
Solve that for d.
S12 = 135
S20-S12 = 210
S20 - 135 = 210
S20 = 345
Now, we know that
S20 = 20/2 (2a+19d)
S12 = 12/2 (2a+11d)
So, we have
10(2a+19d) = 345
6(2a+11d) = 135
Solve that for d.
Answered by
Jay
old how did you get 345
Answered by
Jay
please how did you get 345
Answered by
Jay
OK I see now . sorry I asked
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