athematic progression

1/ We can find the common difference = second term - first term = q-p

Last term = p + (n-1)d = p + (n-1)(q-p) = 2p

Hence n = q/(q-p)

Sum = n(first term + last term)/2 = q(p + 2p)/(q-p) = 3pq/(q-p)

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