Question

Sum of the first n odd number is 625 . What number is n ?

Answer 1

odd number s

1,3,5,7............n terms

a(first term)= 1

d(common difference) = a2 - a1 = 3-1 = 2

sum = n/2 {2a + (n-1)d}

625 = n/2 {2×1 + (n-1)2}

625 = n/2 (2 + 2n - 2)

625 = n/2 × 2n

625 = n^2

n = √625

n = 25