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if the common difference of A. P.is 3.a20-a15

Answer» \xa020 th term a20\xa0= a+(20-1)d = a+19d15 th term a15\xa0= a+(15-1)d = a+14da20 - a15\xa0= a+19d-(a +14d) = 19d-14d = 5d = 5*3=15
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