Question

in an AP a=1,an=20sn=441 find n

Answer 1

FIrst term in A.P = 1

Last term in A.P = 20

Sum of the terms = n/2 ( a + l)  {l represents last term]

441 = n/2(1 + 20)

441*2/21 = n

n = 42

So, n = 42

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