The sum of given A.P.1, 4 , 7 , 10 , . . . upto 20 terms is___________

1.	The sum of given A.P.1, 4 , 7 , 10 , . . . upto 20 terms is____________ .
Answer» a = 1 d = 4-1 = 3an = a + (n-1)da20 = 1 + (20-1)3a20 = 1 + (19)3a20= 1 + 57a20= 58

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