Question 1014351
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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[n]}}} = {{{a[1]}}} + (n-1)*d.

So, 

{{{a[20]}}} = {{{a[1]}}} + 19*d,   (1)

{{{a[50]}}} = {{{a[1]}}} + 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.
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