The Total solution for NCERT class 6-12
Given:
Sum of GP = 381
Where, a = 3, r = 6/3= 2, n = ?
By using the formula,
Sum of GP for n terms= a(rn – 1 )/(r – 1)
381 = 3 (2n –1)/ (2-1)
381 = 3 (2n –1)
381/3 = 2n –1
127 = 2n –1
127 + 1 = 2n
128 = 2n
27 = 2n
n = 7
∴ value of n is 7