SOLUTION: Thr 20th term of an arithmetic progression is 10 and the 50th term is 70, find the first term and the common difference

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Question 1014351: Thr 20th term of an arithmetic progression is 10 and the 50th term is 70, find the first term and the common difference
Answer by ikleyn(52788) About Me  (Show Source):
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Thr 20th term of an arithmetic progression is 10 and the 50th term is 70, find the first term and the common difference
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The formula for the n-th term of an Arithmetic progression is 

a%5Bn%5D = a%5B1%5D + (n-1)*d.

So, 

a%5B20%5D = a%5B1%5D + 19*d,   (1)

a%5B50%5D = a%5B1%5D + 49*d.   (2)

Now, distract (1) from (2). You will get

70 - 10 = 30*d.

Find d from there.

Then think what to do next.