All terms of an arithmetic progression are natural numbers. The sum of its nine successive terms, beginning with the first, is larger than 200 and smaller than 220. Find the progression if its second term is 12.
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Solution
Let initial term be a and common difference be d, given a+d=12
and 200<9a+36d<220⟹200<108−9d+36d<220
⟹92<27d<112⟹3.407<d<4.148
⟹d=4 and the progression is 8,12,16,20,24,28,32,36,40,42,48,52